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.
Apart from the AI pathfinding issues causing disgusting framedrops, this mod is very fun even in it's current state. Luckily, it seems like the developers are working to improve the game in a unique and interesting way, especially with how they integrated the ranking and the tech-tiers.
There are a few kinks concerning AI left to work out so it can't get a 10. But the depth of the mod is brilliant. Each general now actually feels very unique and not just a weak vanilla faction. The new units are skinned wonderfully and everything talks which is very good. I actually quite like the Chinese speaking Chinese and the GLA speaking something Middle-eastern. All in all, a terrific mod and I have tried many Zero Hour mods and this certainly pips them all to the number 1 slot. Phenomenal.