BitTorrent clients allow you to download and upload files using the BitTorrent protocol
Deluge is a full-featured, FLOSS, cross-platform client, featuring full encryption, created to be lightweight and unobtrusive.
qBittorrent is the FLOSS alternative to the non-FLOSS µTorrent client. Fully featured and cross-platform, it also supports full encryption.
Miro follows the all-in-one philosophy of doing things. It is a a Bittorrent client, as well as a podcatcher, integrated with the Miro Guide, which features a wide collection of podcasts. It will also play the music on your PC, convert/transcode many audio/video formats and has built-in support for the Amazon MP3 store.