qBittorrent - Lightweight and open source torrent client that runs on all major platforms.
BiglyBT - BiglyBT is a feature filled, open source, bittorrent client. Auto migrate from Vuze and Azureus. I2P integration, Swarm Merging, Advanced Tag System, WebTorrent support, built-in VPN kill switch, Meta-search, UPnP/DLNA access, and much more.
Deluge - Deluge is a full-featured BitTorrent client for Linux, Unix and Windows.
BitTorrent - BitTorrent is a peer-to-peer program developed by Bram Cohen and BitTorrent, Inc.
rTorrent - rtorrent is a BitTorrent client for ncurses, using the libtorrent library.
Transmission - Transmission has the features you expect in a BitTorrent client: encryption, a web-based interface...