1. It's an Attiny85 based micro controller development board and it is similar to the Arduino line only cheaper smaller and a bit less powerful.
2. With a whole host of shields to extend its functionality and the ability to use the familiar Arduino IDE.
3. The Digispark is a great way to jump into electronics or perfect for when an Arduino is too big or too much.
4. Support for the Arduino IDE 1.0 + (OSX / Win / Linux).
5. Powered by micro USB or external source 5V or 7 - 15V (12V or less is recommended automatic selection).
6. Onboard 100mA 5V regulator.
7. 6 I/O pins (2 are used for USB only if your program actively communicates over USB otherwise you can use all 6 even if you are programming via USB).
8. I2C and SPI (via USI).
9. PWM on 3 pins (more possible with software PWM).
10. ADC on 4 pins.
11. With power LED and test / status LED.