Atmega328p docs

http://www.atmel.com/devices/atmega328p.aspx?tab=documents#!

Pinguino - Arduino-like electronics prototyping platform with PIC microcontrollers.

http://www.pinguino.cc/

Pinguino is an Arduino-like electronics prototyping platform. It supports different 8- and 32-bit ©Microchip microcontrollers, all with built-in USB module (no FTDI chip !).

Pinguino comes with a USB Bootloader. This small program running inside the microcontroller is responsible for transferring your application from your PC to the microcontroller memory and handing over the control to this program afterwards.

No programmer is needed(*), the microcontroller can be reprogrammed over USB with a PC.

8-bit : PIC18Fx550, PIC18Fx5K50, PIC18Fx6J50 and PIC18Fx7J53 family
32-bit : PIC32MX Mips family

Erlang Embedded Buggy

http://www.erlang-embedded.com/2013/10/erlang-plays-pool/
https://github.com/ivaniacono/ebuggy

MAX7219

SPI

Hardware
LedControl lib
LedControl demos

Tutorial arduino max7219 led display driver ic

How to Run an Arduino for Years on a Battery

http://openhomeautomation.net/arduino-battery/
JeeLib library

Shrink Arduino project down to a single 8-pin ATtiny chip

If you have a simple Arduino project that uses only a few pins, you might be able to shrink it down to a single 8-pin ATtiny chip. In this video, Matt Richardson shows you how, based on a tutorial from MIT Media Lab's High-Low Tech Group. The best part is you can use the same Arduino code and development environment that you're already used to.

Arduino blinking example using C

http://www.element14.com/community/blogs/mirandasoft/2013/07/15/beaglebone-black-atmel-avr-development-with-avr-dragon-and-arduino-mega-2560