WS2812 FX library for Arduino and ESP8266
Capture and control API for IIDC compliant cameras
USB Bridge for SMBus/I2C, GPIO, & Clock
Haptic input knob with software-defined endstops and virtual detents
DIY Arduino Boards for IO using port expanders and I2C
Facilino: Block programming environment for Arduino
EventMachine, fast, simple event-processing library for Ruby programs
A keyboard layout that's worth learning.
Quickly rename large quantities of USB drives, just plug in and unplug