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.
Infantry general's jet APC. It is able to transport infantry quickly, but soldiers can not fire from it. One of the advantages is the ability to drive on the mountians and jump from the cliffs.