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.
Here is a sneak peek at what to expect for the Campaign. Made in Adobe After Effects CS5 by me (lil tasman). All briefings will look like this, but respective color tint by what faction you are.