Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Circuit Simulator - Animated electronic circuit simulator using ideal components to visualize voltage and current.
FreeCAD - An open-source parametric 3D modeler
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.
Sculptris - Sculptris: Enter a world of digital art without barriers.
Solve Elec - Solve Elec is a free educational program to draw and analyze electrical circuits.