Avastar is an Addon for Blender 2.67 or newer. The tool is optimized for making Characters & Character animation for SL, OpenSim and similar online Environments.
Primstar is an Addon for Blender-2.6 (or newer). The tool is optimized for creating static content for SL, OpenSim, etc. Primstar-2 supports the creation of Sculpted Prims and Terrain