LDraw - LDraw is an open standard for LEGO CAD programs that allow the user to create virtual LEGO models...
LeoCAD - LeoCAD is a CAD program for creating virtual LEGO models.
Stud.io - Build LEGO designs online with friends.
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