The transmission-daemon is a daemon-based Transmission session that can be
controlled via RPC by transmission-remote (see transmission-utils) and
other Transmission BiTtorrent client such as GTK+ and CLI interface.

Transmission has been built from the ground up to be a lightweight, yet
powerful BitTorrent client. Its simple, intuitive interface is designed
to integrate tightly with whatever computing environment you choose to
use. Transmission strikes a balance between providing useful functionality
without feature bloat. Furthermore, it is free for anyone to use or modify.

WWW: http://www.transmissionbt.com/