Adafruit Trinket 5V is a tiny anad low cost microcontroller board, built around the Atmel ATtiny85, a little chip with a lot of power. The board is designed to be small enough to fit into any project. It is a low cost Arduino IDE programmable board.
The Attiny85 is a useful processor because despite being so small, it has 8K of flash, and 5 I/O pins, including analog inputs and PWM analog outputs. Adafruit Trinket 5V has a USB bootloader so you can plug it into any computer and reprogram it over a USB port just like an Arduino. Also Adafruit has made some simple modifications to the Arduino IDE so that it works like a mini-Arduino board.
Adafruit Web Site