Develop Reference

GWT kind of thing in .NET

Is there is any alternate of GWT in .Net. GWT is basically an API from Google which allows you to code in Java and when the application is deployed, the GWT cross-compiler translates the Java application to standalone JavaScript files that are optionally obfuscated and deeply optimized.
For more details visit :- http://en.wikipedia.org/wiki/Google_Web_Toolkit

You may checkout Script# but to be honest with you those kind of things don't get enough attention in the .NET world as this might be the case with GWT.

From a quick google: jsc, SharpKit and Script#.
However as JavaScript becomes more ubiquitous (and it will node.js etc) it may be worth investing the time to learn to code JavaScript natively.

I don't think so. There are some projects that try to do cross-compilation of C# to JavaScript (ScriptSharp, SharpKit), but I don't think it's the right way to do it.
I would suggest investing the time into embracing the web as it is and trying a MVC-like web framework (KnockoutJS, AngularJS, EmberJS, BackBone).

Converting an existing web app to desktop application

I saw some other similar questions on this topic here but they were not very helpful so I a posing this question.
What is the fastest way to convert a reasonably sized, simple web app to a Java desk top based client targeted for pc and mac? Unfortunately I can not share a whole lot of details about the app here due to various reasons. The most complicated UI in the app though is a page that contains a multi level threaded discussions (please see here for an illustrative example of what I am talking about.) The current web app is based on python so I can not re use anything from the server side code (dont think this is an issue)
I have never done any swing or awt or any other Java based thick client GUI work. My thinking is more or less defined by web based applications. I am capable of doing end to end web app development (including backend and decent UI using HTML, CSS and JS) using Java or python. For your answers please focus on Java solutions only.
So here are my questions
What is the best framework or tool I should use? I found some of the following tools on the web as part of my research.
Awt - does not look like this is a good choice.
Swing which I believe is bundled with regular Java SDK/JRE. - This may be my best
bet.
SWT which seems to compliment Swing in some fashion.
Griffon based on an article here. This framework uses Groovy ( I
have no clue about Groovy, btw) Adobe Air flex. Any open source
frameworks?
What are some of the other issues that I need to keep in mind? Some that I would like your comments on are:
How does the fact that it needs to be deployed on the client complicates things? Since we are using Java, I believe this to be a non issue. I am aware of the usual trade offs between a web based app and a desktop app (e.g. ease of deployment and upgrades etc etc.)
How easy is it to create a one click installer and bundle the app and the environment needed - eg. JRE etc?
The product needs to work on Mac and Windows. Does that complicate things in any way (Again, since it is Java I am assuming there are no gotchas but would like to be forewarned if there are any)
What is the framework or technology that may be good to have on the resume as a skill set?
My deadline is a max of 2 months - would that be enough for a reasonably simple web app given that I need to learn all of these technologies? I am just trying to get a sense here - I know it is most likely impossible to give an accurate answer - just assume I am smart enough and can pick up any unfamiliar tech stack fast enough.
Thank you!

GUI toolkit
Given "Mac and Windows", I'd say that settles my recommendation as "Swing" (perhaps with SwingX1).
I agree with your assessment of AWT. It does not support formatted text in any component out-of-the-box. It also lacks trees, tables (and other components) & people with recent experience using it. Note though, that it is also "bundled with regular Java SDK/JRE" just like Swing, it is just that it is older and less enabled than Swing generally.
If anything complements Swing it would be SwingX. SwingX is built on Swing and provides advanced controls that are not available 'out of the box' in the J2SE.
Swing and SWT are mutually incompatible - use one or the other.
I have no experience with Griffon.
Swing is the most used of the options outlined, so for getting help (ignoring other potentially important factors in the decision), it would be a good choice.
Note 1) Add SwingX if they have any groovy components that present threaded conversations easily, but I suspect a JTextPane would suffice.
Deployment
As far as deployment goes, that is a little more tricky than it seems. Many desktop computers do not come with Java as standard. Those that already have it, might have an old version.
To ensure a JRE of the right minimum version to run the app. is available, use the deployJava.js (mentioned, with links, in the JWS page below).
To provide a 'one click' launch experience for the user, look to Java Web Start.
Cross-platform gotcha's
Unfortunately, though Java is x-plat, there are plenty of things that programmers can do that stuff that up. E.G.
Not accounting for the platform default:
File encoding (file.encoding2)
Line break (line.separator2)
File separator (file.separator2)
Coding fixed size ('absolute layout') apps. that will be shown as different sized apps. on other OS.
...
Note 2. That is showing the property to use for each.
Timetable
Obviously I cannot speak for you, but I can tell you that I would have had no chance of going from 'which technology' to a 'deployable app' within two months.
Hope you're more capable than me! ;)

You said that you wanted a Java solution, but be aware that there are plenty of Gui options in Python, and you already have your web application written in Python.
Groovy is a different programming language than Java, but Groovy runs on the JVM. Do you want a Java solution or a JVM solution? I ask because you mention Griffon.
Assuming you want Java, I think your main options are Swing, SWT, JavaFX 2, and Apache Pivot. Oracle has said that they intend for JavaFX to replace Swing as the GUI platform of choice. That said, JavaFX 2 is in its infancy, and only a preview release is available for Mac right now. The upshot of JavaFX and Apache Pivot is that you could use the same code for your web application as your desktop application.

You can try doing so in small steps:
* As a first step you can create an applications with SWT and embed your application in a browser control.
* Then you should move pages and some controls from the web app to the desktop one by one.
In this way you can get a minimal application in hours :)
P.S. If you want an iOS app with this approach it's worth looking at this open source project: http://en.wikipedia.org/wiki/PhoneGap

Google Web Toolkit vs Straight Javascript for reasonably large & complex application?

I've got a web conferencing client written predominantly in Java/Swing with some JNI native modules for stuff like: video, audio, and desktop sharing. In total the client is about 400k lines of Java code not including native modules.
We are investigating a long term plan for migrating away from Java/Swing and toward HTML5/Javascript for the client. As of right now, browser support is shaky/non-existent for some of our needs such voip, web cam video, and desktop sharing. So in the short term we could perhaps ship a browser plugin to do these things along with HTML5/JAvascript to do everything else.
For something of this complexity (basically a rich desktop client being ported to the web) what would make more sense: GWT (Google Web Toolkit) or straight Javascript using a JS library such as jQuery ?
EDIT: There are currently 5 developers working on this project.

If you have programmers with Java background, there are plenty of reasons why to use GWT:
powerful statically typed language also #client side
rapid development (!!!)
tools! IDEs, PMD, FindBugs and gazillion other. Also configuring Eclipse with Google plugin is just piece of cake, unlike many other frameworks.
permutations for various browsers are already handled by GWT itself
your JavaScript is optimized - handled by GWT
you STILL CAN use plain JavaScript if you want (however GWT is designed the way you don't have to)
GWT is really scalable. Your Java back-end will stay true Java, so you can use whatever favorite powerful java libraries
client side development is quite robust and Swing-like, not too hard to find a programmer to fit there
And many others. Honeslty, JavaScript is still quite slow (okay not to troll - language doesn't have "speed", but you get me). It doesn't matter if you are using jQuery or GWT. Face it, it isn't going to perform as fast as thick client. So why to sacrifice your comfort :)

Take the google wave product as an example. It was merged from plain old javascript to GWT to support more rapid development, especially considering the many developers concurrently working the project.
In my experience, manually hacking a site of what you're suggesting with jQuery would be an awful lot of work which most likely will suffer from refactoring issues, difficulty to reuse code, and probably end up with alot of code that will be really hard to grasp for any new developers coming into the team.
Don't get me wrong jQuery is really great javascript tool; but when writing complete applications in it, it quickly becomes unmanageable. That's at least my opinion.

From my experience, GWT is great for developing web applications where the intent is to mimic the look and feel of a desktop application. The fact that your team already seems to have plenty of Java/Swing experience would make this migration path easier than directly moving to a pure-JavaScript solution.
Using pure JavaScript to build a desktop-style web application, you'll be finding yourself searching for or using a lot of libraries/toolkits/plugins/widget builders (even with the use of jQuery) just in order to get the basics down. These basics can easily be provided by GWT.

What are the options for developing powerful browser hosted UI in Java?

I am interested to widen my horizons and wish to learn what are the options for developing a powerful browser hosted UI in Java. All I know is .NET based solutions, specifically Silverlight, which I find extremely powerful, although not without some regretful omissions as compared to its elder brother - WPF.
So, to rephrase my question. Are there mature Silverlight alternatives in Java?
Thanks.
P.S.
I am not starting the war of Java vs .NET, so please do not raise the benefits of Java against .NET in general. I am interested in a specific area only, anything else is put aside.
Please, do not bring Adobe AIR, flex, HTML5, etc... The questions is about Java.

The question is about Java, but front-ends for the web are almost never written in pure Java.
GWT - that's where you write pure Java which is then translated to javascript and html automatically
JSF - you reuse rich components to create your pages. Still there's html and javascript. This resembles the ASP.NET model
Vaadin - heard of it, never used it. Seems promising
ZK - Same as above.
jQuery - yes, this has nothing to do with Java, but is very powerful tool for creating rich UI
Flex - easy integration with Java back-ends. (I personally don't like Flex, but it's a viable option)
(I specifically omitted JavaFX, because in my opinion it is not yet mature)

You know, having rich applications in the browser using Java has existed since, say, 1999 : applets, that's what they're for.
They were long far from beautiful. However, with the recent apparition of JavaFX, they can now have a very nice look.

The closest thing to Silverlight in the Java world is JavaFX. I haven't worked with it myself though, and I don't think I've randomly come across any sites using it in the wild... which means your users are less likely to have whatever plugin is required... and you're likely to be cutting out most mobile users too. (I believe there's a mobile flavour of JavaFX, or at least one planned, but you really want to find out whether it exists on iPhone/Android/(whatever your target market is).
Personally I would probably try to stick to HTML 5 and JavaScript, which can still be pretty rich. (That doesn't necessarily mean writing all the UI by hand, of course - projects like GWT and jQuery are your friends.)

Open Laszlo is worth a look they have a nice interactive demo section too.
The OpenLaszlo platform consists of the LZX programming language and the OpenLaszlo Server:
LZX is an XML and JavaScript description language similar in spirit to XUL, MXML, and XAML. LZX enables a declarative, text-based development process that supports rapid prototyping and software development best practices. It is designed to be familiar to traditional web application developers who are familiar with HTML and Javascript.
The OpenLaszlo Server is a Java servlet that compiles LZX applications into executable binaries for targeted run-time environments.

I'm not sure if it fits your demand but have you looked at the Google Web Toolkit? It compiles Java to javascript and some colleges have made nice UI's with it.

I've used GWT before and more recently Vaadin which I would recommend. You can give it a go at a demo sampler here. I am currently using it to create custom portlets for the Liferay CMS/Portal and I am pretty happy with it.

How to rapidly build a Web Application?

To build a Web Application, what kind of open source web application frameworks / technologies are currently present that would be:
Faster to learn.
Ease of use.
Have widgets for rapid development(From a GUI perspective).
Database integration.
I would want this web app to communicate to a Java client.
I am not bound to Java on the server side and free to try out any good rapid application framework.
To summarize, I haven't done much work for the server side hence am not conversant with the tools and technologies for the same.
What would you suggest?
Any and every input would be welcome!...

There is no single "right" answer to this question. As a Java programmer of some 10+ years when asked this question my usual answer is... PHP. There are several reasons for this:
Low resource usage (Apache, nginx);
Cheaper hosting;
Really low barrier to entry;
It's really Web-oriented rather than being general purpose that can be used for Web (like Java);
The fact that PHP scripts aren't persistent (like Java servlets are) between requests makes them much more forgiving and less likely to cause memory leaks and other problems;
No deployment step (like Python, Perl, etc). I'd say this is about the best thing about dynamic scripted languages. Just save the file and click reload on your browser;
PHP might be inconsistent in syntax and several other things but it's also mature and used by some really large sites on the Web (eg Facebook, Yahoo, Flickr, Wikipedia);
PHP is by far the most popular Web development language.
Widgets can be done by any manner of Javascript frameworks like YUI, ExtJS, SmartClient, jQuery UI, etc;
PHP fits well with MySQL.
That being said, a lot of these apply to other languages too (eg Python/Django).
I don't think you necessarily need a framework for PHP but if you do I'd look at one or more of:
Kohana: it's like a more modern version of the more popular CodeIgniter;
Zend Framework: it's modular so you can use as much or as little of it as you like;
Smarty: it's a powerful templating system.

Django has a few notable 'rapid' items including automatically generated administrative interface, bundled ORM (lowers dev time by not having to write SQL and some other code), and a large community with several re-usable apps.
Where Django (or Ruby on Rails or any other MVC framework for that matter) isn't going to be rapid is the learning curve when you first come to developing on them. Django (and RoR) have quite a bit of seperation-of-concerns and if you're not used to that sort of environment, it takes a while to learn the framework. If you're using an ORM that's something to get used to as well, and then of course for any framework you go with there's the API to learn as well.
PHP on the other hand is a little more intuitive in terms of where you put the code and how pages make up your web app. It'll basically let you slap code wherever you want so in the beginning it will probably be faster. In the end it will be quicker but your final product will be sloppier and probably require re-factoring later on.
This comes down to a question of what's the use of the framework. If it's for a hobby site, just go with what's easy (php), otherwise you might want to consider a well-supported MVC framework.
As others have pointed out, jquery is probably the pick for pre-made GUI widgets.
Edit -- And apparently now Django (as of 1.1) has a very awesome set of unit testing tools it comes bundled with. Things like an extended TestCase specifically for Django, a test client (you can do test page request w/o an actual client or server), a tool to give you a % of test coverage you have of the project, and a bunch of other neat stuff.

You've already tagged your question with "java", "php", "python", and "ruby-on-rails", so researching and learning more about those tools would probably help to answer your question.
However, I believe that rapidly building an application is almost never actually the correct goal. Normally, what you want to do is build an application that can be rapidly maintained -- that is, maintained with the lowest possible overall development cost over time.

I would say part of the learning curve will go into understanding concepts. I have been learning about web-apps for some months now, and with my improved understanding of concepts right now, most frameworks show very much similarities. Here are my results so far:
PHP: Great to learn about concepts for doing forms, http-post-requests, http-get-requests. easy interaction with database layer, and it is possible to obtain a working basic application in couple of hours. Almost no hassle with build-systems and web-server configuration.
Ruby-on-Rails: Great to learn about REST and more complicated CRUD applications. Great to learn about the complexity behind MVC and especially simple and powerful interaction with the database layer by using ActiveRecord. Introduction of meta-programming (code-that-writes-code, code-scaffolding) is great. Nice opportunities for free cloud-deployment, e.g. heroku.com and there is a very active community
Java: Powerful interaction with web-server possible (Tomcat, JBoss, ...) MVC is rather complicated here, and in general many configuration-steps necessary (build systems, ORM layer, ...) Grails is a great simplifaction and introduces meta-programming for Java. Jboss Seam introduces REST for Java (but have not looked into this yet)

There are tons, which ones are "good" depend on what you need.
There's Ruby on Rails, which is pretty handy.
For python there's django.
For PHP (I spend a lot of time dealing with PHP), you can look at:
symfony
cakePHP
Solar
Zend Framework
Which are all good in certain situations, and annoying in others.

Speaking only in terms of speed of development, Ruby on Rails is the fastest one out there.

I would vote for Grails.

You can build an runnable Java Web application within 5 to 10 minutes by using the following online Java web application generator:
http://www.webappexpress.net