So, search google.code or git or wherever and you will find:
lots and lots of good intentions and well wishing but I've yet to find one that is viable or even modifiable for iOS development (except the Arianne engine)
So with that said... I'm going to develop a Cocos2d based RPG engine(1), it will NOT be open source. You will however be able to purchase a license to develop your own RPG games.
More information and I'll be updating the LoH (Legends of Hylore) web site.
(1)Engine: will have the ability to read plists and provide actions based on configuration data.