KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.
FreeCAD - An open-source parametric 3D modeler
Fritzing - Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to...
Sculptris - Sculptris: Enter a world of digital art without barriers.