WinMX

I know it's not as quick as torrents, but there's two reasons I'm still smitten with WinMX.
Firstly, it's a passive, patient application: it rewards those who are willing to wait and encourages an open sharing of files. I like that, rather than the frenetic ratio-counting world of torrents.
Secondly though, and mostly, it's so sweet because it's now completely autonomous. Since the RIAA shut down WinMX in September, it has been revived by its users. It's now got no centralised body at all for RIAA to attack. (Theoretically, they could go after users, but as a) it's pretty difficult to identify users with WinMX and b) they would be using an application they claim is illegal to track people anyway! then that seems unlikely.)
The users have taken over the means of production, it's a little bit of true online anarchy.
It's a beautifully distributed, example of Out of Control software. So it may not be the best application in the world, but it's showing us the direction of the future!