I've written a couple of libraries for Java game development that a few people use.
Slick is a 2D games library for Java. It's layered over the top of LWJGL which provides high performance OpenGL rendering for 2D games. Slick a easy way for developers who have used Java2D to make use of OpenGL. It also provides a framework for games, sound and input support and many utilities to make us highly efficient in producing quality games
Phys2D was a quick port of Erin Catto's original Box2D demo source that he presented at GDC (this was way before Box2D became the wonderful library it is today). Phys2D provides a much nicer and productive API over the top of Box2D but does lose some efficiency on the way. Phys2D has grown to provide multiple collision strategies and various different primitives.
When JBox2D came out I'd pretty much considered my work for Phys2D finished. JBox2D has better performance and closer to the new Box2D library. However, I was pointed at a few people wanting the "nice" interface on Phys2D back - so I wrote a library to wrap round the speedy JBox2D and give that nice interface. Fizzy was born!
Years ago, a friend asked me to make it easy for Java users to play OGG files through Java Sound. As easy as Clip! So, I built this library and a few people have found it useful since.