OpenTyrian is a port of the DOS shoot-em-up Tyrian. Jason Emery
generously gave the OpenTyrian developers a copy of the Tyrian 2.1
source code, which has since been ported from Turbo Pascal to C.
The port uses SDL, making it easily cross-platform.

Tyrian is an arcade-style vertical scrolling shooter. The story is
set in 20,031 where you play as Trent Hawkins, a skilled fighter-pilot
employed to fight Microsol and save the galaxy.