Gearbox is a simple command-line bittorrent client written in Rust. It is currently very much a work-in-progress and I wouldn't recommend actually using it. It may have all sorts of horrible bugs that format your hard drive or frighten your cat. That being said:
Gearbox supports Linux and OS X.
To build Gearbox, you will need a recent nightly version of the rustc compiler and the Cargo build tool. You can find these here.
Once you have those installed, you can just run cargo build (or
cargo build --release if you want to compile with optimisations) to build the
executable.
Just run
path/to/gearbox path/to/torrent_file.torrent