Ryzom, the MMORPG that open-sourced its code a while ago, is now free to play.
Their forums are down right now, but I’ve heard that they are going to do something along the lines of micro-transactions. Supposedly that makes more money than subscription, so we’ll see if that helps them survive. It would be a bummer to see a company open up their software and then go out with a whimper. They have a lot of activity on their dev site, so hopefully that contributes to their appeal.
I myself would love to get the world editor working on a non-Windows machine, because it is a pretty decent editor, and being able to import new buildings could really contribute to a nice platform for gaming of all sorts. If we put something together like the Neverwinter Nights Community Expansion Pack, and got a workflow for exporting out of Blender, I could see this blowing up.
And if they worked on armor/weapons, you could actually use it run virtual tabletop games…