If you haven't heard of Fallout: Project Brazil, what you need to know is that it's a fan made total conversion that looks to provide a prequel story to Fallout: New Vegas (cause, you know, there totally weren't any official games that did that). Set in the LA Boneyards and San Bernardino Mountains - an area roughly the size of Fallout 3's Capital Wasteland - a few years after the defeat of the Enclave by the Chosen One (spoilers, sorry), you play as an inhabitant of Vault 18 (a never before mentioned vault which seems to be obsessed with American Football) who is forced out of the vault by forces beyond his control, eventually becoming entangled in the conflict between the Enclave Remnants, NCR forces, Tribal Independants, and the Super Mutants.

That is, you'll get to do all that in the full release. At the moment, the only real part of the game on offer is the sections within Vault 18 itself - which they describe as a small world unto itself - with about 7 hours of gameplay for completionists. The outside world is coming in a later update, but if you're down for 7 hours of running through a vault being a dick to everyone you meet (cause who doesn't do that at least once in a Fallout game), you can grab the current build of Project Brazil from both the New Vegas Nexus or Mod DB. Enjoy.