Several times within this blog I reported about Croquet. It was written in Squeak Smalltalk and supported communication, collaboration, resource sharing, and synchronous computation among multiple users. Basically it was a followup of ideas from Morphic - but all in 3D. You could create and visit portals to interactively collaborate.
If I remember correctly it was later open sourced and ended up in OpenCobalt.NET - there are still some infos are on the Squeak wiki and a video on Youtube.
It was also continued as OpenQwaq platform and used to form solutions for a company named 3dicc
(started by Ron Teitelbaum, David A Smith and Andreas Raab).
Now it seems there is a fully new web based implementation of these historic ideas available. It is called ARCOS - Augmented Reality Collabroative Operating System and if you check it out you will find many similarities.
You can try it instantly in your browser using the following link or watch the following videos for a demo: