via the ananialog
The XOrduino is a stripped down low-cost Arduino-compatible board that plugs right into the XO’s USB ports. But wait, there’s more: it’s also compatible with the Scratch Sensor Board, so you can use this device to control Scratch (and Turtle Art?). It should be compatible with the Arduino IDE and all Arduino Leonardo-compatible shields.
There are only 20 components needed for basic Arduino functionality, costing $5 from digikey (in quantities of 100 or more). Local labor or even older kids could assemble this by hand.
The XO Stick is for when $5 per student is too much money. Based on the AVR Stick and the ATtiny85 processor, it costs only $1/student. It’s not as user-friendly as the Arduino-compatible board, but can be used to teach simple lessons in embedded electronics.
Eagle design files on github: