Teensy USB Development Board...

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The Teensy is a complete USB-based microcontroller development system, in a very small footprint, capable of implementing many types of projects. All programming is done via the USB port. No special programmer is needed, only a standard "Mini-B" USB cable and a PC or Macintosh with a USB port.
https://www.pjrc.com/teensy/

Programming the Teensy
https://learn.adafruit.com/usb-snes-gamepad/programming-the-teensy


http://hackaday.com/2013/12/09/meet-the-teensy-3-1/

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More switches (I2C example)
The Teensy 3.1 has 34 pins, but what happens in you need more, or can’t use all the pins for buttons because some are needed for LEDs? One option is to use a matrix of switches which I will cover in a different article. But an exceptionally cool way is the use the I2C bus. ...
http://teensyhauptwerk.wordpress.com/2014/01/17/more-switches-i2c-example/