Odamex is a free, cross-platform, modern client-server Doom engine
A free 3d game for PC that does not limit the player. Fight,Build,Gain
Source code of the chapters of the book 3D Game Development with LWJGL
A minimalist and cross platform System Shock source port
486 lines of C++: old-school FPS in a weekend
A Java light, open source first person shooter,with editors.
Zombie survival on a city wide scale!
Complete, Fast, Accurate, Game Boy/CGB/SGB Emulator.