Wikipedia
Tribler
Tribler is an open source decentralized BitTorrent client which allows anonymous peer-to-peer by default. Tribler is based on the BitTorrent protocol and uses an overlay network for content searching, which makes the program operate independently of external websites and renders it immune to limiting external action such as government restraint. Due to this overlay network, Tribler does not require an external website or indexing service to discover content. The user interface of Tribler is very basic and focused on ease of use instead of diversity of features. Tribler is available for Linux, Windows, and OS X.
Tribler also features a built-in video streamer known as SwarmPlayer.