The 'Bus Pirate' is a universal serial interface created by Hack A Day and made into a kit by Fundamental Logic. The bus pirate can interface with most serial interfaces (SPI, I2C, RS232, JTAG, 1wire, etc) and is controlled by a simple serial terminal. If you have a bus pirate and a pc with a serial port, you can talk to most serial chips.
This is the pre-programmed micro-controller including the latest firmware and serial boot-loader. If you purchased a kit, the kit already contains the micro-controller. Purchase this is you're sourcing your own parts or would like a spare part.
For more information, look to the bus pirate kit documentation or the Hack A Day Bus Pirate page.