Engine for Collaborative Science Education MMOG?

plisdku asks: "My research advisor wants to create an online, collaborative science education game for middle- to high-school students; we need a 3D engine! A pioneer in internet-assisted laboratories (iLabs), he has developed real experiments that students can operate remotely over the internet. We envision a game where students wander a campus, solving Caltech-style 'stacks,' and learning collaboratively as they perform the great experiments of the history of science in simulated and real laboratories. What we need is a 3D engine and content creation system with which our team of artists and bright student developers can produce a prototype within a year. Requirements: customizable avatars, flexible integration with other technology (iLabs, CompEdu, etc.), and reasonable licensing fees (open source would be great). Our last project used SGI tools -- what are our modern-day options?"