FreeCAD - An open-source parametric 3D modeler
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
QCAD - QCAD is an application for computer aided drafting in 2D.
Onshape - Onshape is the first full-cloud 3D CAD system. It runs in a web browser and on any mobile device.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Sculptris - Sculptris: Enter a world of digital art without barriers.