UCI chess engine
Yet Another Chess ENgine
A java-based, purely object-oriented chess engine.
"Kenny" is an XBoard/WinBoard chess engine based on "Winglet"
Chess game interface
3D OpenGL Chess - C++
Tyrannus is a Chess GUI and Engine built in Java.
one more chess engine in the barn
Anni is on free open-source C# UCI bitboard chess engine
The Java Chess Engine