Modrex is a project to integrate all of the realXtend features with the mainline OpenSim code by incorporating them in a optional regionmodule – hence the project name modrex. The work is being done by Adam Frisby. The stability of the code is surprisingly good.
The RealXtend viewer employs the open source OGRE game engine and differs from the Linden Lab viewer (LLviewer) in several ways. The most distinct difference is in the new rendering potential offered by OGRE. When using RealXtend as a viewer for OpenSim, one obtains real-time shadows, improved lighting simulation, and more importantly, the OGRE mesh. The mesh is hierarchical (multiple meshes and sub-meshes) and can include a skeleton for defining avatar motion and dynamics.
ModRex (source code) while not part of the viewer, is the glue that connects the viewer to the opensim trunk code. Version 0.5 of realXtend released on 30.6.2009 is featuring ModreX for the first time.