A small Arduino library for GSM modules, that just works
OSI Layer 2 driver for nRF24L01 on Arduino & Raspberry Pi/Linux
An Arduino NeoPixel support library
Open source framework simplifying the creation of C++ applications
MIDI for Arduino
EtherCard is an IPv4 driver for the ENC28J60 chip
Electronic design and programming tools suite like Eagle, MpLab
An automatic, configuration-less, GUI for Arduino projects.