The BitTorrent protocol provides one of the fastest ways to download large files from the internet, but to take advantage of it you need to install a torrent client. Transmission is one such client and it benefits from an extremely small resource footprint as well as the fact that it is incredibly easy to use.
The client is written in objective-c which means, on a Mac, that it integrates tightly with OS X and uses Growl notification and dock badges to keep you informed about the status of the program. Besides speed and low resource requirements, Transmission includes everything you would expect to find in a torrent client.
In addition to the program itself, there is also a web interface for download management, peer exchange, support for magnet links, global and torrent by torrent speed limiting and much more.
One of the key benefits of Transmission over other torrent clients is the number of add-ons that are available. Browse through the add-ons directory and you will find everything from the ability to control torrents from your mobile to an updated web interface and much more.
There are a number of torrent clients to choose from, but Transmission's speed and extension options means that it is well worth a look.