Just read this on RockOnFlash, amaaaaazing.

"PaperWorld3D is a Realtime 3D Multi-User Application Framework built for the Flash Platform."

and.....it's opensource

* Creating modular game components which can be created, shared, edited, updated and extended by anyone with some knowledge of flash.

* Skinning mechanism allows designers to create new or replace exisiting graphical assets wihout touching any code.

* Multi-lingual content, allows users to choose a language to view the game in and switch languages at run-time.

* Connecting to and communicating with Red5 to allow multiplayer interaction and communication, database access or connection to any other application running on your server.

* AI - Steering Behaviours, Decision Making etc. etc. allow you to create complex behaviours for NPCs.