Hammer of Thyrion (uHexen2) is a cross-platform port of Raven Software's Hexen II source. It is based on an older linux port, Anvil of Thyrion. HoT includes countless bug fixes, improved music, sound and video modes, opengl improvements, support for many operating systems and architectures, and documentation among many others.
...It mainly aims to implement exciting new features, cars, tracks and AI opponents to make a more enjoyable game for the player, while constantly pushing forward visual and physics realism. It is also intended for any research, study or teaching activity, around physics and AI, thanks to its GPL V2+ license, and the clear and modular architecture of its C/C++ code base.