First, its written in Smalltalk - Squeak specifically.

It uses OpenGL for 3D rendering - offloading most of the heavy lifting to hardware accelleration.

It supports 3D user interface creation via some fairly trick modeling tools (draw a picture - then inflate it).

It has a new scripting language/UI framework called Tweak which is massively multi-threaded (every event is forked to a new Smalltalk process). This is kind of new and will require some tuning I think (I've been playing with it for a month or so). It works but there are probably lots of optimization opportunities.

There is a distributed event synchronization protocol called TeaTime which makes it possible to distribute the 3D worlds around the network. You can create a world, then create a portal to someone elses world. Think of portals like hyperlinks on the web.

Its still a work in progress but its been in development for at least a couple years.