Croquet is a 3D, GL-accellerated collaboration environment built to run under the
Squeak Smalltalk VM.
It "was built to answer a simple question. If we were to create a new operating system and user interface knowing what we know today, how far could we go. What kinds of decisions would we make that we might have been unable to even consider 20 or 30 years ago, when the current set of operating systems were first created."
To view screenshots, you'll need the ability to view the
documentation PDF.
Not my cuppa, but everyone else seems to want to play Quake with their spreadsheets. Props to 'RG' for the link.