What is it?

This is an adapter board that allows you to perform AVR programming with Raspberry Pi GPIO pins. The board includes a 3 position switch to allow you to provide target power at either 3.3 volts, 5 volts or self-powered. To protect the Raspberry Pi, the power is supplied through an AP2331 current limiting switch. This should allow you to hot-plug the target without any risk of transients causing your Pi to reboot. The programming pins of the target are connected through a level-shifting bus buffer chip so that programming will work at any (reasonable) target voltage. The programming pins are also held at a high impedance state (virtually disconnected) when programming is not taking place, so that the programmer won't interfere with normal operation of the target. Lastly, there is an LED that will turn on when programming is taking place (when RESET is held low and the programming signals are active).

You get the board, a shrouded 6 pin DIP header and a 26 pin stacking header. Both of those come unattached, so you must solder them on yourself, but all of the surface mount components are pre-assembled.