This is the famous Atmel ATtiny85 microcontroller, specifically the 20MHz Attiny85-20PU. This is a popular AVR microcontroller based on RISC architecture, and packs a decent set of functions despite its size and low number of pins.

Check out the SparkFun Tiny AVR Programmer for using with this IC.

Features

• Atmel 8-bit AVR RISC-based microcontroller
• 8KB ISP flash memory
• 512B EEPROM
• 512-Byte SRAM
• 6x general-purpose I/O lines
• 32x general purpose working registers
• 1x 8-bit timer/counter with compare modes
• 1x 8-bit high speed timer/counter
• USI
• Internal and external Interrupts
• 4-channel 10-bit A/D converter
• Programmable watchdog timer with internal oscillator
• 3x Software selectable power saving modes
• DebugWIRE for on-chip debugging
• Achieves a throughput of 20 MIPS at 20 MHz and operates between 2.7-5.5 volts.

Resources

• Datasheet