The Ur-Quan Masters: Open-source remake of Star Control II
I played Ur-Quan Masters for the first time earlier this year. Despite its age, I found it to be one of the finest games that I'd ever played. The story, in particular, is just perfect, and has just the right mixture of seriousness and comedy, very much in the same style as another (even older) classic, Starflight. Being able to build the game from source and read through the code was a nice bonus.<p>I highly recommend checking it out; if you can get over the rather dated graphics and gameplay mechanics then you'll find this to be a real gem.