Thunder Brigade
Thunder Brigade is turn-based tactical tank battle game. The player and the computer control a number of tanks, both sides trying to eliminate the other or capture the goal.
Trichromic
Mixing 1 part Command & Conquer, 1 part Starcraft, 4 parts Advance Wars, and 4 parts wacky original design yielded this gem: Trichromic. Choose to lead one of three distinct armies...
UFO: Alien Invasion
It is the year 2084. You control a secret organization charged with defending Earth from a brutal alien enemy. Build up your bases, prepare your team, and dive head-first into combat.
Warzone 2100
Warzone 2100 is a real-time strategy game in a post-apocalyptic setting that was developed by Pumpkin Studios. It was one of the first real-time strategy games in 3D.
Widelands
Widelands is a free open source (GPLed) real-time strategy game. It is built upon the SDL and other open source libraries and still under heavy development.