ElectroDroid Pro
Circuit Calculators
Electronics Student Reference
Arduino Simulator DIY Safely
Motors for Makers: A Guide to Steppers, Servos, and Other Electrical Machines
Arduino: Complete Beginners Guide For Arduino - Everything You Need To Know To Get Started (Arduino 101, Arduino Mastery)
Electric Circuits (Stick Figure Physics Tutorials)
Encyclopedia of Electronic Components Volume 1: Resistors, Capacitors, Inductors, Switches, Encoders, Relays, Transistors
Make: More Electronics: Journey Deep Into the World of Logic Chips, Amplifiers, Sensors, and Randomicity