Attiny85 Digispark USB is the smallest Arduino compatible development board so far. Originally developed under the name Digispark and released under open source license. It has 6 port with several functions. Depending on the programming (with Arduino IDE) can it have 6 digital I/O, 4 analog inputs or 3 PWM outputs. It can be powered by a USB port or an external power supply of 6…35V DC.
Attiny85 Digispark USB specs:
Support for the Arduino IDE 1.0+ (OSX/Win/Linux)
Power via USB or External Source – 5v or 7-35v
On-board 500ma, 5V Regulator
6 I/O Pins
8k Flash Memory (about 6k after bootloader)
I2C and SPI (vis USI)
PWM on 3 pins (more possible with Software PWM)
ADC on 4 pins
Power LED and Test/Status LED
For more information, please follow the link to the official Digispark product page: klick here.