uTorrent is a free BitTorrent client, the Mac version (officially still in beta) of the popular, open-source uTorrent client for Windows.
Much like the lightweight uTorrent for Windows (also weighing in at less than 5MB), this version of uTorrent excels at downloading files quickly with minimal resource overhead. Even more stripped down than the Windows version, uTorrent for Mac gives you a familiar, three-pane interface, with support for multiple downloads and probably more drill-down details than you even need--including graphs, tables, and other specifics on seed, peers, pieces, and more. You can also throttle upload and download rates, and stop seeding automatically at a certain ratio. uTorrent is probably not the best client for actually finding torrents (there's just a simple search bar that takes you to results pages in your browser), and users looking for browsing and viewing features should check out more full-featured BitTorrent clients.
If you don't need a lot of extra features and you're looking for a fast BitTorrent client that requires almost no configuration, uTorrent is a solid option.