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.
Another thing for Cybernetic general is Vorta. Vorta is a secondary supplies gatherer. Half of the price of Harbinger, but it also brings half the amount of supplies. It is faster and can be used well in some critical situations where you need smaller amount of money but faster.