This is just the microcontroller burned with the USBtinyISP firmware code. If you're buying a kit, this is included. This is intended for people who are buying just the PCB or are experimenting with the kit and want a backup chip.
"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering" - Freeman Dyson