People are doing some crazy things with OpenMW, there is a huge Star Wars total conversion mod for OpenMW called Starwind for example. Basically a complete game.
I've only just played a bit of Starwind so far, but been in more of a fantasy mood so I've been exploring Tamriel Rebuilt.
There is also home of the Nords which adds a part of Skyrim, and there is another mod that so far adds an island of the coast of Cyrodiil called Province Cyrodiil.
>Starwind Never heard of this until now cool, I love Morrowind and KOTOR so I'll have to check it out at some point. I replayed Morrowind a few years ago (vanilla with a few bugfix and QOL mods I don't think I used OpenMW) and it was a great experience. I did install Tamriel Rebuilt as well after I beat the game and explored a little of the new area but I was so overpowered at that point and was just levitating everywhere while invisible so I kind of got bored and quit, seems like it'd be better to explore it early or midgame.