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 ...
Stud.io - Build LEGO designs online with friends.
Mecabricks.com - Mecabricks is an online LEGO building tool.
MLCAD - MLCad LEGO Cad Software