
Circa 20 years ago I was interested in running an UO shard, at the time I was testing RunUO, it seemed modern at the time because C# and .NET were only a few years old :)
I see they haven’t updated the text on the website in 2 years ;)
The only drawback was the inability to port the software over to other operating systems. However projects like MONO are working extremely hard to provide a very capable .NET framework for the alternative operating systems.
Somebody should tell them about the new multiplatform .NET. Seriously though, I’m surprised that website is still online.

Maybe OP is playing it off a cassette player like on C-64 ;)