The ATtiny85 module is a great option for running simple Arduino programs, it's small, cheap and relatively easy to use. If your project requires only a few simple inputs or outputs, then this is ideal module.

Features: 

• support for the Arduino® IDE
• power via ubs or external Source (pinheader)
• onboard 5 V regulator
• built-in usb
• 6 I/O pins
• 8k flash memory (about 6k after bootloader)
• I2C and SPI
• PWM on 3 pins
• ADC on 4 pins
• power LED and LED on P1