qBittorrent is an easy to use, good looking, and featureful but
lightweight C++ / Qt4 Bittorrent Client.

Note that from version 3.3.15 you will get a warning on startup that
qbittorrent has a new way of saving things. If you want to backup your
old config directory first, you will find it here:

~/.config/qBittorrent

That way you can return to an older version by swapping directories
around.

This is the last version of qBittorrent that will build with Qt4
libraries.  You might want to embrace the future with Qt5 and newer
versions of qBittorrent. See the qbittorrent-qt5 SlackBuild for more
information.