Scott Blum is one of the Atlanta Google engineers leaving next week, but he mentioned on his Google+ page that their group was allowed to open-source parts of what they were working on for the past year. "I'm happy to say that one of the things I'll be celebrating is that we were able to liberate portions of our last year of work as a new open source project. It's called "Collide" (collaborative IDE), and is a web-based collaborative code editor."
However, the public code-base for Collide at this point isn't the full-featured web IDE they had running at Google, but is stripped-down. "What we pushed out is extremely stripped down right now, but the most interesting tech stuff around collaborative editing is all there. Long term, we hope it will serve as a catalyst for improving the state of web-based IDEs."
The code for the Collide collaborative web-based integrated development environment is being hosted on Google code. The Collide Collaborative IDE depends upon Java 7 and Ant as external dependencies while everything else is bundled-in. According to the members of the Google Code page, there were many Google engineers responsible for this work.