There's also now an open source recreation of the original client, all written in C# that actually uses a GPU so it renders 4k at 250fps instead of 800x600 at 12.5fps. It's a very mature and stable reproduction at this point.
Over 2k active players daily (edit: by active I mean there are over 2k players logged in and playing at any given time). The devs are incredibly active, and there is a lot more to do here than original UO.
I tried playing uo outlands, but what really struck me was the lack of bugs. Tbh my favourite part of playing uo back in the day was exploiting bugs so uo outlands isn't really for me
https://github.com/classicuo/ClassicUO