I'm not sure if you're aware of these titles but there are remakes of Privateer and Star Control 2 released as freeware and Fish Fillets is now released as freeware. I've also found a RTS named Glest which is also freeware.
http://priv.solsector.net/
http://fillets.sourceforge.net/
http://www.glest.org/eng/index.htm
http://sc2.sourceforge.net/
I haven't tried Glest or the remake of Privateer. But the other two are great games and I doubt that the remake of Privateer can be bad
