<In 2000, Raven Software released the source code to their class based shooter game Hexen II and its multiplayer extension HexenWorld.
Since then, there has been some source ports of this game, such as the now discontinued Anvil of Thyrion project, but nothing has been done for Linux since the beginning of 2002.
The Hammer of Thyrion project is a cross-platform source port effort: developed for Linux, BSD and Mac OS X people, with continued support for Windows users as well. Many bugs are fixed and even new features are added: New sound modes, improved mouse handling, improved video modes, OpenGL glows and more. You can go to project page for more information.