LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.
FreeCAD - An open-source parametric 3D modeler
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
SketchUp - 3D for Everyone
ARIS Express - ARIS Express is based on the proven ARIS methodology and industry standards.