LeoCAD - LeoCAD is a CAD program for creating virtual LEGO models.
LDraw - LDraw is an open standard for LEGO CAD programs that allow the user to create virtual LEGO models...
LDCad - LDCad is a multiplatform ...
LPub3D - LPub3D empowers you to make LEGO-styled developments on your PC, alongside point by point direction manuals.
Mecabricks.com - Mecabricks is an online LEGO building tool.
MLCAD - MLCad LEGO Cad Software