This is a Linux port of the 1995 shooter, from source recently released by 3D Realms. The game engine is free, but you need datafiles from the shareware or full commercial version to play.

The Story:
You are part of an elite group of operatives called HUNT (High-risk United Nations Taskforce), and you must stop a maniac cult leader from killing millions of people. While scouting a remote island, you are suddenly surrounded by enemy troops with guns blaring. In the distance you see your boat--your only chance to escape--explode into matchsticks. In front of you is a huge fortress monastery, and your only chance to stop the madness. You are e quipped with awesome, high-tech weaponry like heat-seeking missiles, split missiles, and the Flamewall cannon, which leaves a trail of charred skeletons in its wake. You'll also find magical instruments and weapons so incredible they defy description.

License: free

Additional System Requirements: SDL, SDL_mixer