Iron Seed
This rather unusual sci-fi strategy game that had originally been released as shareware can be found at the official website of the original developers, who are now working on a remake:
Iron Seed Downloads and Manual
Latest game patches
Theseus - Return of the Hero
A follow-up of
Alien Shooter with a different protagonist, and running on the same engine. The game was released for free by Sigma Team at some point, and is available from their website:
Download Theseus - Return of the Hero