OpenRA

OpenRA (Open Red Alert) is an open source real-time strategy game engine based on a reimagined version of early Westwood real-time strategy games. It implements Command & Conquer and Command & Conquer: Red Alert as mods, with later updates adding official support for Dune 2000. They are not just clones of the original games, but updated reimaginations with rebalanced gameplay, new units and using modern technology in the background. The assets from the original games can be installed through existing copies or by downloading them from the OpenRA servers, with the exception of Dune 2000 which was never released as freeware and can only be installed from the original discs. The engine itself is released with the GPL 3 license.