If you like playing with gadgets like me you will love this one. It’s very tiny (as the name implies) and as of version 3.0 it is Arduino-compliant. If you install Teensyduino addon on top of Arduino IDE you can compile and upload your sketches to Teensy just like Arduino. This tiny things rocks a 32-bit ARM Cortex-M4 processor.
Also it is quite cheap and it’s size allows it to be used in a variety of projects. Strongly recommended for gadget-lovers.