Contra is a freeware modification for Command and Conquer Generals: Zero Hour real-time strategy game. It's a big project started in 2004. It adds many new units as well as numerous new upgrades, new general's powers and buildings. It also adds new sounds, maps, bug fixes, enhanced graphics, and other effects, as well as three new generals. There are lots of people playing in multiplayer.
This mod is one of the best, but there is always room for improvement, like fixing common errors (game crash errors, mismatch and lag), though some errors can´t be helped, there must be a way to make the mod so it minimizes the errors, if the Contra team can manage that, they truly have earned themselves a 10, as this mod is nothing if the game can´t be played.