Teensy 3.2 is a small, breadboard-friendly development board designed by Paul Stoffregen and PJRC. Teensy 3.2 brings a low-cost 32 bit ARM Cortex-M4 platform to hobbyists, students and engineers, using an adapted version of the Arduino IDE (Teensyduino) or programming directly in C language.
This latest version of this complete USB-based microcontoller development system now adds a more powerful 3.3V regulator, as well as accepts a wider voltage input range. This board has the same size, shape and pinout as well as full compatibility with all shields and add-on boards made for the Teensy 3.1, plus double the Flash memory as the Teensy 3.0.
Note: Teensy 3 and 2 are not official Arduino-brand products. Although the Teensyduino IDE has been adapted so that many simple Arduino projects will work with the Teensy, there will still be a lot of libraries and shields that will not work with this device.
Teensy Official: http://pjrc.com/teensy/teensy31.html
Adafruit Product Page: https://www.adafruit.com/product/2756