essentially, the software is free if you don't charge your players; otherwise, they take a very (in I men very) small cut of the profit. The Firefly MMO will be made on this engine.
There's also Realcrafter. $50 for the individual indie kit; however, I have heard a lot of bad things about this.
These are both 3d, but I'd sudgest going with MultiVerse. I have it on my machine now to play around with it, and so far it's possibilities are limitless.
