My first question when I first read about the OPC amp, was a fairly common one apparently: "is it an amp, or is it a computer?". In short, it's both, but essentially it's a PC that is tailored towards the needs of modern musicians. I won't go in to too much detail, as the duo of Doug Doppler (check out his awesome work here) and Charlie Cooper (the brains behind the amp) do a fantastic job of explaining it.
There are some really great design features on the OPC, which make it functional as an amplifier and a computer, as it has been built from the bottom up with guitarists in mind.
So if you want to know more, check out the video, with every bit of technical spec (hardware and software), and a full demonstration of the amp's capabilities.