While not being open source, BitTorrent Inc. does promote the open standardization of the protocol[1], and employs the creator of bittorrent, Bram Cohen[2], as chief scientist.

μTorrent is, I think, the best suggestion for a client for people who need client suggestions. (having tried a large number of very mediocre competitors, free, open, or otherwise)

I usually stick to rtorrent on the commandline, but that's a shitty suggestion for helping bring awareness to hacker issues.

1. http://bittorrent.org/ 2. http://en.wikipedia.org/wiki/Bram_Cohen

Personally, I think qbittorrent is a better general suggestion.

http://www.qbittorrent.org/

I've used both utorrent and qbittorrent and the only difference is the latter does not have any ads bundled.

They are not the Free Software Foundation!

If anyone is looking for alternative, Deluge is open source and very good (http://deluge-torrent.org/)