Warzone 2100 is an open source real time strategy game similar to Command and Conquer
In Warzone 2100, you command the forces of "The Project" in a battle to rebuild the world after mankind has almost been destroyed by nuclear missiles. The game offers campaign, multi-player and single-player skirmish modes. An extensive tech tree with over 400 different technologies, combined with the unit design system, allows for a wide variety of possible units and tactics.
Warzone 2100 was created by Pumpkin Studios, published by Eidos Interactive and is currently developed by the Warzone 2100 Project.
Read more and download
You can download a portable version of Warzone 2100 (Version 2.3.2) from Portable apps - here