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
DIY Arduino Board
How to make a schematic you can post. - Introductory Tutorials - Arduino Forum
How to Read the Arduino Schematic Diagram | LEARN @ CIRCUITROCKS
Arduino Tutorial by Manmohan Pal: How to make Arduno Uno Board
Simulate Circuits Online: Circuit Simulation Made Simple | Elektor Magazine
LED Flasher | Flash Twenty LEDs Using Arduino - | Full Electronics Project
Create your own custom Arduino like circuit - Electronics information from PenguinTutor
THE DIY ARDUINO BOARD FOR 5$ : 8 Steps (with Pictures) - Instructables
How do you make pretty arduino schematics? - Project Guidance - Arduino Forum