Realmcrafter:
-created by a bunch of unknowns using the Blitz engine.
-Anywhere from 50 - 100 USD for license
-Can only make a MMORPG
-Been in development for about 4-5 years and still not fully released.
-AFAIK flat file system for it's database


Multiverse:
-Created by the people that made Netscape and ausing a Java backend
-100% Free to use while you don't charge; percentage when you do charge
-Can make any MMO
-Has been in development for ?? and somewhat fully released
-MySQL database.

You decide.