qBittorrent is an opensource BitTorrent client for sharing and downloading files from torrent sites.

rTorrent is a text-based ncurses BitTorrent client written in C++, based on the libTorrent libraries for Unix.

Deluge is a lightweight, Free Software, cross-platform BitTorrent client.

Folx is a download manager for Mac OS X. It integrates with the Mozilla Firefox, Safari and Google Chrome web browsers and with the FlashGot extension.