UFO doesn't stand for Unidentified Foreign Object. No, it stands for Ultimate Follower Overhaul and it's an essential Skyrim mod for PC.
UFO brings a mind-boggling number of changes to the game's various companions. We aren't going to list them all here but if you're interested in reading a huge change log, you'll want to head on over to this site to run down the changes.
If you don't want to, know that it comes with new dialogue options, ups the number of followers, and riding horses for followers. That's just a taste.
This is an outstanding Skyrim mod and we'll be fortunate if it makes an appearance on the marketplace for console.