rtorrent is a BitTorrent client for ncurses, using the libtorrent library. The
client and library is written in C++ with emphasis on speed and efficiency,
while delivering equivalent features to those found in GUI based clients in an
ncurses client.

Configure options are stored in ~/.rtorrent.rc; a well-commented base 
can be found at /usr/doc/rtorrent-0.8.0/rtorrent.rc

This requires libtorrent, which is also available from SlackBuilds.org