Fallout: The Frontier is a mod for Fallout: New Vegas that takes the franchise, unofficially, to the post-apocalyptic wasteland of Oregon, and has been in in the works for over three years now. This week, the mod officially released and is now available to download.
The mod includes an impressive amount of new content, including three new main storyline quests set in Oregon, with a huge number of side quests, and "tens of thousands" of lines of new dialogue. Perhaps the most impressive addition to the game's engine is driveable vehicles, which alone is something of an impressive technical feat.
The map is also pretty huge, being roughly the size of the Mojave desert in New Vegas, and even boasting more interior spaces than the New Vegas plus it's DLC combined. In summary, this basically a brand-new Fallout experience.
You can find out more at the mod's official website.