No, it's some sort of a plug-in. It's amazing, you download a 8mb file and install it, then you have the full quake with everything in it and it never loads, downloads or anything. Can be played in windowed or fullscreen mode, has console and everything... Honestly i am amazed at what they've done.
It also has friends system with integrated IM sorta thingy, full online stats tracking, server browser, etc. For the moment there are UK and NL servers only but later on there should be servers everywhere.