Transmission-utils includes the tools to create and manipulate torrent files.

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/