Onshape - Onshape is the first full-cloud 3D CAD system. It runs in a web browser and on any mobile device.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Sculptris - Sculptris: Enter a world of digital art without barriers.
FreeCAD - An open-source parametric 3D modeler
meshmixer - meshmixer is an experimental 3D modeling tool for making 3D mashups without too much hassle.
OctoPrint - OctoPrint is the snappy web interface for your 3D printer that allows you to control and monitor all aspects of your printer and print jobs, right from your browser.