At Sun Labs' open house today, we talked to Nicole Yankelovich who's working on research project MPK20: Sun's 3D Virtual Workplace. MPK20 (which includes Wonderland's 3D graphics engine and the the demo world) is available as open source and built on top of Sun's own gaming server (Darkstar) to simulate a virtual world a-la Second Life. The Silicon Valley company is also looking to open source project Darkstar. At the beginning of the year, Second Life's maker, Linden Labs, open sourced its viewer application and promised do the same for its server side application. Yankelovich also mentioned Open Croquet as another open source virtual world engine.