Dr. Scott Ananian, from the One Laptop Per Child (OLPC) project, conceived an Arduino Leonardo-compatible board especially designed for the OLPC XO laptop, with the goal to cut down its price as much as possible, to foster its adoption even in developing countries. From Scott’s blog:
The board, named XOrduino, is open hardware (schematics and pcb files can be found on github), and can be directly plugged into the XO’s USB ports, which allowed Scott to save the money required for the USB connector. Moreover, its design has been inspired by other open hardware projects, such as SparkFun’s ATmega32U4 breakout board and SparkFun’s Scratch Sensor Board-compatible PicoBoard.
Scott designed also a second board, which is even cheaper than the first one, called XO Stick:
It’s very exciting to see how open technologies, such as open hardware and open source software, contribute to the way education and creativity can take place around the world, especially regarding their promotion in developing countries.
For more detail: Arduino-compatible board for the OLPC XO laptop