Invision - Prototyping and collaboration for design teams
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Plant - Version control app and plugin for Sketch
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
FOLIO - Simple version control app for designers based on Git
Sculptris - Sculptris: Enter a world of digital art without barriers.