It might be 2013 and Warzone 2100 was published in 1999 but it was one of the best games of it's time. But since then, it's had it's own open source development, with a ton of new features and a new release! You command the forces of The Project in a battle to rebuild the world after mankind has almost been destroyed by nuclear missiles.
The open source Warzone 2100 offers a campaign, multi-player, and single-player skirmish modes. An extensive tech tree with over 400 different technologies, combined with the unit design system, this allows for a wide variety of possible units and tactics.
Only a few days ago 3.1.0 was released to the public which contained a massive 2 1/2 years worth of bug fixes and improvements. So what are you waiting for? Hurry up and play :)