Other notable features:
- Hosted Browser Environment ( a sandbox so to say )
- Browser History Management
- Async RPC Calls
From my 5 minute review, the Toolkit comes with extended documentation including a 'Getting Started' guide to get you up and running quickly, an Internet Explorer control, class references and a commandline utility to create Eclipse projects.
Instead of 'forcing' the developer to learn yet-another-UI-language ( XAML/MXML/XUL ) it let's you stay in Java to write UI code. Whether or not that is the best approach is something i won't go into.