Bespin — an experiment from Mozilla Labs that possibly will propose an open, extensible web-based framework for code editing that aims to increase developer productivity, enable compelling user experiences, and promote the use of open standards.
At this time we have initial working experimental prototype that we can use to understand concepts of Bespin and the possibilities that it opens up.
The protorype includes support for basic editing features, such as syntax highlighting, large file sizes, undo/redo, previewing files in the browser, importing/exporting projects.
As for me idea of web-based code editor is arguable due to we have enough excellent standalone open-source code editors like Netbeans [http://www.netbeans.org/] or Eclipse [http://www.eclipse.org/] that have good collaboration possibilities. Standalone code editors we can develop using pretty object-oriented languages like Java and don’t bother with Javascript. But time will say its word.
Mozilla wants you
The Bespin experiment is still in its infancy and just getting started. There are many ways to join the team and get involved: [https://bespin.mozilla.com/]