compatible, take it as 5 I/O (2 shared with USB) Arduino main board. There are several tutorials ready for you. not to forget the User's Manual.

Features:
ATtiny85 on-board, 8K of flash, 512 byte of SRAM, 512 bytes of EEPROM.
Internal oscillator runs at 16MHz.
USB bootloader so you can program it with the modified version Arduino IDE (from DigiSpark), or
With Cytron Arduino 3rd Party Boards URL, you can use the latest Arduino IDE.
Micro-B USB jack for power and/or USB uploading, you can put it in a box or tape it up and use any USB cable for when you want to reprogram.
Accorcding to DigiSpark, it is supported on All OS (Linux, Mac OS and Windows), yet we can only tested it on Windows.
~6K bytes available for use (~2K taken for the bootloader).
On-board 5.0V voltage regulator with 800mA output capability and ultra-low dropout. Up to 15V input, thermal and current-limit protection.
Power with either USB or external output (such as a battery).
On-board green power LED and red pin #1 LED.
Reset button for entering the bootloader or restarting the program. No need to unplug/replug the board every time you want to reset or update!
5 GPIO - 2 shared with the USB interface. The 3 independent IO pins have 1 analog input (ADC) and 2 PWM output as well. The 2 shared (USB) IO pins have 1 more analog inputs and aPWM output.
Hardware I2C / SPI capability for breakout & sensor interfacing.
Works with many basic Arduino libraries including RainbowBit library.
Comes with mounting holes.
Super small and Cute of course!
* Avoid using the shared IO (pin 3 and 4) during program loading as it may affect the USB communication.
 
Tutorials:
CuteDuino USB Tutorial
Modify Arduino IDE for CuteDuino
Repairing CuteDuino Bootloader
Arduino Gemma on CuteDuino
Cytron Arduino 3rd Party Boards URL - Adding CuteDuino into Arduino IDE 1.6.4
CuteDuino's pinout diagram:

Getting Started with CuteDuino: