Tutorial #1-Introduction to Arduino - Design-Build-Code: Engineering Projects
A Guide To The World Of Arduino
ARDUINO - Digital Design
Circuit design software that makes it easy to design, document, and debug electronics projects for the breadboard (more info in the comments). Would you find this useful? (x-post with r/ArduinoProjects) : r/arduino
Circuit Design App for Makers- circuito.io
Arduino UNO Reference Design | 3D CAD Model Library | GrabCAD
Collaborative Design and Creative Expression with Arduino Microcontrollers (MIT IAP 2017) | Andrew Ringler
NERO-SP1 - Bridgetek - Reference Design Board, Arduino UNO Compatible Board, Short Shield Pins
Arduino and Genuino brand refresh, design insights | Arduino Blog