Deluge is a full-featured  BitTorrent client for Linux, OS X, Unix and Windows. It uses libtorrent in it's backend and features multiple user-interfaces including: GTK+, web and console. Deluge features a rich plugin collection; in fact, most of Deluge's functionality is available in the form of plugins.

Deluge was created with the intention of being lightweight and unobtrusive. It is our belief that downloading shouldn't be the primary task on your computer and therefore shouldn't monopolize system resources.

Features:

Core/UI split allowing Deluge to run as a daemon

Connect remotely to the Deluge daemon

Web UI

Console UI

GTK+ UI

BitTorrent Protocol Encryption

Mainline DHT

Local Peer Discovery (aka LSD)

FAST protocol extension

µTorrent Peer Exchange

UPnP and NAT-PMP

Proxy support

Web seed

Private Torrents

Global and per-torrent speed limits

Configurable bandwidth scheduler

Password protection

RSS (via Plugin)

Other  libtorrent features

And much more!