The Freespace Source Code Project has yielded some pretty cool results. It's amazing how they've improved how the 10 year old games look. What was a muddy looking ship is now a high polygon wonder.
Not to mention there are some good mods out there. Transcend, Sync, and Homesick were fun to play. Also, that's what that Star Fox fan game is being made from.
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Also, while I think it's dead, there was a cool Star Wars mod for Homeworld 2 and that was fun to play around with just to see the Star Wars ships blasting the hell out of eachother.







