Tyrian is a computer game developed by Eclipse Productions (later named World Tree Games) and published in 1995 by Epic MegaGames.

The game was officially released as freeware in 2004, and the graphics have been made available under an open license in April 2007.

More Information here: http://en.wikipedia.org/wiki/Tyrian_(computer_game)

Now it turned up into Open Tyrian, since it’s been re-implemented to use SDL (check project here: http://code.google.com/p/opentyrian/ )

Kalimerou ported the engine to the GP2x, but you still need the original game files.