The Digispark is an Attiny85 based microcontroller development board similar to the Arduino, only cheaper, smaller, and a bit less powerful. With a whole host of shields to extend its functionality and the ability to use the familiar Arduino IDE the Digispark is a great way to jump into electronics, or perfect for when an Arduino is too big or too much. It can be programmed on the Arduino IDE with Arduino compatible code. It is perfect for use in projects where the Arduino UNO/Nano are too big and minimal IO pins and functionality are required. The Digispark is available in two variants -with USB Connector and without USB Connector. This board comes without the USB Connector is is suitable for projects which require a small PCB. Being a very popular platform, multiple tutorials, guides and sample codes are available on the internet which help you get your projects running with it. The Digispark is shipped fully assembled except for the two included and easy to solder headers. Here are the specs:

Specifications:

Support for the Arduino IDE 1.0+ (OSX/Win/Linux)
Power via USB or External Source - 5v or 7-35v (12v or less recommended, automatic selection)
On-board 500ma 5V Regulator
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)
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