Cloud9 Collaboration mode is also open source: https://github.com/c9/c9.ide.collab https://github.com/c9/c9.ide.collab (Same code that's used on http://c9.io ht

Cloud9 Collaboration mode is also open source: https://github.com/c9/c9.ide.collab https://github.com/c9/c9.ide.collab (Same code that's used on http://c9.io http://c9.io which can be used for free). Has chat and ability to work with multiple files out of the box.