Ur-Quan Masters is an open source port of Star Control II:
(FROM http://uqm.stack.nl/wiki/Star_Control_II):
Star Control II, the sequel to the original Star Control, is a space adventure game that features role-playing elements alongside a robust 2D combat system. It was a milestone for non-linear gaming and an undeniable influence on modern space travel games such as Homeworld; many consider it one of the best computer games of all time. The player assumes the role of the captain of a single starship wandering a detailed environment of solar systems, gradually gathering information and resources in order to defeat a mysterious and implacable enemy; the plot contains numerous mysteries and other half-explained elements that contribute to the beauty of the game,1 along with a rare sense of humor that manifests numerous times, inevitably having the player rolling on the floor laughing.