[pwg]

RTorrent https://pmukhanov.wordpress.com/2014/01/19/installing-rtorre...

Text console based, so it can run headless and/or in the background in a screen/tmux session.

[diyorgasms]

I've been using rtorrent for years and I wouldn't ever suggest anything else. It's just so damn simple and reliable. I love the concept of watch directories too. Upload a torrent file to a specific directory, and the data will be downloaded to a specific directory. You can have multiple watch directories for different types of data.

[anonova]

Note that rtorrent is no longer supported by homebrew[1]. You'll have to build it yourself with gcc since it can't be compiled with clang.

[1]: https://github.com/Homebrew/homebrew-core/pull/369

[ciupicri]

Transmisson can also run headless.