LDraw - LDraw is an open standard for LEGO CAD programs that allow the user to create virtual LEGO models...
cmftStudio - GUI counterpart of cmft - cross-platform open-source cubemap filtering tool.
LDCad - LDCad is a multiplatform ...
open3mod - A free, Open-Source 3D Viewer designed to make it all easier. Massive 3D Format support
Stud.io - Build LEGO designs online with friends.
Online 3D Model Converter - free online 3D model converter, upload a model and export it into popular formats