meshlabMeshlab, the popular open-source mesh manipulation package, has just released version 1.2. MeshLab is used for editing, cleaning, and filtering of large unstructured triangular meshes, like the type generated by 3D Scanning equipment for STL systems.  Version 1.2 contains several bugfixes along with new tools for mesh segmentation, mesh optimization via user selectable metrics, and advanced rendering.

SourceForge.net: MeshLab.