Transmission

According to the developers: Transmission doesn’t bundle toolbars, pop-up ads, flash ads, twitter tools, or anything else. It doesn’t hold some feaures back for a payware version. Its source code is available for anyone to review. They don’t track users, and their website and forums have no third-party ads or analytics Uses less CPU than any other GUI client, including some non-GUI clients Transmission also has the lowest memory footprint of any major BitTorrent client Transmission has the features you want from a BitTorrent client: encryption, a web interface, peer exchange, magnet links, DHT, µTP, UPnP and NAT-PMP port forwarding, webseed support, watch directories, tracker editing, global and per-torrent speed limits, and more.