Tale of Two Wastelands is a mod that combines both Fallout 3 and Fallout New Vegas, and is considered by many players to be the definitive way to enjoy frolics through the wastelands both of Washington DC and New Vegas, and now the popular mod has received it's much anticipated 3.2 release, which totally rebuilds the mod from scratch.
The rebuild has been three years in the making, and has a changelog so long I doubt the SQL limit will accept it verbatim in this article, but suffice to say, there's so many improvements and changes, it's well worth updating if you're using this mod.
The mod allows you to play both Fallout 3 and New Vegas from the New Vegas engine, allowing you to keep the same character, and items, between both and bringing mechanics such as weapon mods to the Fallout 3 universe.
The only downside is that it's unlikely to work with other mods, and you need a clean copy of both Fallout 3, New Vegas, and all the DLC to get this to work, but for many, the benefits far outweigh the drawbacks.
You can download the new version from the mods official site, here.