The Ur-Quan Masters is an open source port of Star Control II.

From Wikipedia:
Star Control II: The Ur-Quan Masters is a critically-acclaimed science fiction computer game, the second game in the Star Control trilogy. It was developed by Toys for Bob (Fred Ford and Paul Reiche III) and originally published by Accolade in 1992 for PC; it was later ported to the 3DO with an enhanced multimedia presentation, allowed by the CD technology. The source code of the 3DO port was licensed under the GNU GPL in 2002. The game still enjoys a cult following.