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.

PicoTorrent is a tiny BitTorrent client for Windows with low memory usage, high performance and a native user interface.

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

Halite (named after the mineral) BitTorrent client based on the excellent libtorrent library.

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.