Vaadin basically provides the building of RIAs through server side java based on GWT using a sophisticated Architecture. For a jumpstart on it check out these slides and this video

Technical aspects

IDE

• Eclipse plugin
• Netbeans plugin
• no IntelliJ plugin yet (althoug people got it to run)

Deployment

• The same Vaadin application can be deployed to a Servlet Container, JEE Application Server, Portlet Container or Google App Engine

GWT-Compilation

One of the drawbacks we experienced when using GWT are the rather long GWT-compile times

• GWT-compilation is only required when installing a new Add On or when creating a new GWT-based widget. This will only happen occasionally.

Client/Server communication

In Vaadin the communication is handled based on a UIDL (User Interface Definition Language)

• UIDL based on JSON
• client- and serverside API available
• no writing/generating of boilerplate code
• not too easy too influence
• not heavily scalable as almost every event clientside event will immediately result in a server request

Widgets

• rich widgetset available (out-of-the-box)
  • TreeTable is under development. Some live demos here
  • CKEditor Wrapper (see related links for demo)
• add ons can easily be integrated
• effort for creating new widgets is higher than with pure GWT

Development

• Development speed is huge
• Easy to use Reflection i.e. for creating dialogs

Testing

When writing a Vaadin application you'll only fit together the server side widget-types (Window, Form, Layout, Button, TextField, etc.). The have no compile-time dependencies to any GWT-related class.

• your UI-code can easily be tested with standard JUnit-TestCase

Non technical aspects

Community & momentum

• there's about 40 contributors - 10 of them having more than 100 commits
• User rating is 4.8/5

Sources of information

• on the Vaadin homepage there's links to a wiki, forum (by 4th of august 2010: 12434 posts of 958 participants in 8 categories), blog, chat & Twitter
• there's a whole book provided by the developers.

Licensing

• Apache Software License 2.

Additional Information

Performance / Memory Consumption

From what we know so far the biggest disadvantage of Vaadin could be the performance or memory consumption. Here's a few links about this topic

• Optimizing Sluggish UI
• Server-side RIA Scalability
  • Thread discussing above results
• Thread on clientside code size

Simulation

For simulating slow connections you can use sloppy. First tests (using 236k (Edge) bandwith) gave the impression, that - at least for the demo app "VaadinProject" - startup time was considerably slower.
Once the app was running performance was surprisingly good. These tests should be repeated on a more realistic sample app...

Integration with a RESTful API

• An example of integrating Vaadin with a RESTful API

Theming

Here's two examples of available themes

• Reindeer
• Chameleon

References

• Thread on who uses Vaadin
• Experiences made at BlackBeltFactory

Demos

• official sampler
• book examples