Translucent and shaped windows in core Java
The lack of support for translucent and shaped windows has been a subject of quite a few complaints about AWT and Swing. This has finally been addressed in the latest 6u10 build.
Here is how a translucent window looks like:
And here is a shaped window:
And here is a translucent and shaped window:
For more (unofficial) information on where these APIs are located and how to use them, click through to Pushing Pixels.