Vuze (formerly Azureus) is a free BitTorrent client. Developed by Azureus Software, Inc.
License: Freemium
Apps available for Mac OS X Windows Linux Android BSD
Halite (named after the mineral) BitTorrent client based on the excellent libtorrent library. Developed by Eóin O'Callaghan
License: Open Source
Apps available for Windows libtorrent Discontinued