Yep. I agree Pollando. I have been watching one particular developer but that project seems to have come to a halt. Plus the "commercially" available stuff like RealmGen are really crappy. Besides that if you want to have more than a world with like 5 different mobile types then you end up paying a ton of money and their basic scripts are so bad that they're what you'd expect from a free server.
You might check out
http://www.fantasyrealmonline.com. Chris the Avatar has been developing a client/server system. He was originally going to sell it but in the last few posts he's made he's been making noises toward releasing it as an open source project. His last post was in July of this year so I am not sure about the status of the project. In that post he said the first official release was close to being ready. Unfortunately I don't know what format the graphics files will be in. However he is supposed to be creating or have created a map and terrain editor.
I still don't understand why it is so hard for people to pool their resources together in creating some system. I suppose it's a matter of being able to let someone else have a piece of the action plus the desire to have something done your own way. Both attitudes I understand completely. It would speed things up a bit if we could overcome those tendancies however but then again we are all human too.
*grins*