KTorrent
Homepage
Interface: GUI
Written in: Qt4/C++
KTorrent is a full-featured, graphical BitTorrent client for KDE. It has a rich interface as well as support for magnet links, plugins, stopping/pausing and resuming downloads, extended torrent and peers information, system tray integration, plenty of configuration options. KTorrent is definitely one of the most powerful graphical clients for the BitTorrent protocol.
Transmission
Homepage
Interface: GUI
Written in: GTK3/C
The nice fact about Transmission is that it offers both a GTK and a Qt interface, as well as a command-line client for the terminal only. The Qt interface is written in Qt5, and it’s cleaner and simpler than the interfaces from other clients. All the usual features are included in Transmission, so it makes for a good, maybe a bit lightweight alternative to Deluge.
Deluge
Homepage
Interface: GUI
Written in: PyGTK/Python
Deluge is a GNOME BitTorrent client that bundles many features, including the usual ones like stopping and resuming downloads, bandwidth capping, system tray integration, plugins, creating torrents. It is designed based on the client-server model.
Tixati
Homepage
Interface: GUI
Written in: GTK2/C
When it first starts, Tixati will show a window where you can configure basic options, like the default download folder and optionally enable bandwith capping for downloads and uploads. Tixati is pretty complex regarding features, having support for magnet links, integrated chat, web interface. It is highly configurable, with plenty of options to be found in the Settings window.
Vuze
Homepage
Interface: GUI
Written in: Java
Formerly known as Azureus, Vuze’s approach differs a bit from other clients, having a section of free-downloadable videos in HD called the Vuze HD Network. Here you can get HD videos for free.
qBittorrent
Homepage
Interface: GUI
Written in: Qt4/C++
qBittorrent is a Qt client which allows you to open and create torrent files, has support for magnet links, system tray integration, stopping/resuming downloads, capping bandwidth, statistics, and an included RSS reader. qBittorrent also comes with a version that can be controlled via a WebUI, called qbittorrent-nox, running without the need of an X server.
CTorrent
Homepage
Interface: CLI
Written in: C++
This is a command-line BitTorrent client written in C++, fast and simple to use. You can run it as ctorrent torrent_file.torrent and quit using Shift+Q.
rTorrent
Homepage
Interface: TUI
Written in: ncurses/C++
rTorrent uses ncurses for its interface, runs in a console, and needs a bit of time to get used to. With very powerful features, rTorrent is a good choice for the terminal.