TopSpice is an integrated electronic circuit design system with multiple capabilities, including schematic capture front-end, mixed mode simulator, graphical representation, and library of over 35,000 device models.
KiCad: A cross-platform, Open Source suite for electronics design automation that effectively manages schematic capture and PCB (printed circuit board) layout.
Tinkercad is a free, easy-to-use app for 3D design, electronics, and coding. It's used by teachers, kids, hobbyists, and designers to design and make anything.
SketchUp is an easy-to-use web-based program that will help you learn to create 3D models of houses, sheds, decks, home additions, woodworking projects even spaceships.