Multiverse is what you need
The Multiverse Platform makes developing your online game or virtual world a whole lot easier, with an easy-to-use development suite containing plenty of starter content, code and extensive documentation.
Open Source
Every line of code is freely available, so you can do what you want, whenever you want.
Intuitive Interface
Content-creation is incredibly easy, with the simple-to-use yet sophisticated Multiverse Tools set.
A Full Starter MMO
SampleWorld is a fully-functional MMO that you can either use as a reference, or adapt to suit your own needs