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.
M113 APC is a new unit for Air Force general replacing Avenger. Available at rank 1. Strong vs. infantry, light vehicles and aircraft. Can transport 4 soldiers.