Open Cobalt is a free and open-source software platform for constructing, accessing, and sharing virtual worlds both on local area networks or across the Internet, with no need for centralized servers.

By using a peer-to-peer-based message passing protocol to reduce reliance on server infrastructures for support of basic in-world interactions across many participants, Open Cobalt makes it possible for people to hyperlink their virtual worlds via 3D portals to form a large distributed network of interconnected collaboration spaces.

With no licensing fees, users and developers can also freely build and share highly capable multi-user virtual workspaces, game-based learning and training environments, or even just create places to meet and interact with friends.

[1] In early 2008, and with the support of the Andrew W. Mellon Foundation,[2] Julian Lombardi and Mark P. McCahill, at Duke University, launched the community-based software development effort to build Open Cobalt as an open-source virtual world browser application and construction toolkit.

In May 2008, Lombardi was awarded a National Science Foundation grant[3] to further strengthen the community-based software development effort and bring the Open Cobalt virtual world browser to its alpha release.

The goals of the Open Cobalt effort are to stimulate the use of distributed virtual environments, advance visual simulations, and deepen collaboration in education, research, and personal entertainment - and in so doing to: Open Cobalt is both an end-user application and full featured software development environment for creating a rich network of end-user created interlinked virtual worlds.

Open Cobalt's software development environment enables programmers to enjoy the capabilities of a true late bound, message sending language.

Open Cobalt's reliance on Squeak's generalized storage allocator and garbage collector makes it highly efficient in real-time and allows reshaping of objects to be done safely.