Cobalt is an open source virtual world browser and construction toolkit application being developed at Duke University. Cobalt makes it possible for people to easily create, publish, access, and participate in a network of linked virtual worlds. Currently in pre-alpha and built using the Croquet open source software development platform, Cobalt uses peer-based messaging to eliminate the need for virtual world servers and makes it very simple to create and share secure virtual worlds that run on all major operating systems.