A full-featured java BitTorrent client program.
Bit Torrent offers fast downloads and Azureus makes it really easy to use Bit Torrent ! Includes numerous invaluable features for both beginners and advanced users including multiple torrent downloads, queuing/priority systems (on torrents and files), start/stop seeding options, instant access to numerous pieces of information about your torrents and an embedded tracker. This latest version has some new features including a wizard to simplify sending a link to content to a friend or to embed in a web page and an auto upload speed feature.
For Mac OSX, downloads for Windows and Linux are available from this site.