To Dev & Viewers

Sorted alphabetically. Please leave your comment on updates.

Data
Google SketchUp: 3D objects repository.

Viewers
OnRez Viewer: Second Life viewer.

Virtual worlds' frameworks
Croquet: Open source consortium-driven.
Metaplace: Not finalized.
Metaverse: Open source engine.
Multiverse: Netscape veterans for MMOs.
Ogoglio: Web-oriented.
OpenSimulator: Open SL-like (IBM involved).
Papervision3D: Flash 3D.
Project Wonderland: Build worlds with Sun technology.
Solipsis: Still alive?
Unity3D: Used by Fusion Fall.