Blender - Blender is the open source, cross platform suite of tools for 3D creation.
LDraw - LDraw is an open standard for LEGO CAD programs that allow the user to create virtual LEGO models...
SelfCAD - SelfCAD is an online 3D modeling and slicing software.
LDCad - LDCad is a multiplatform ...
SketchUp - 3D for Everyone
Stud.io - Build LEGO designs online with friends.