BitTorrent

BitTorrent is a peer-to-peer program, first developed in mid-2001 by Bram Cohen and BitTorrent, Inc., to use for uploading and downloading files under the BitTorrent protocol. In the protocol, a "Tracker" hosts information about any active computers which are trying to share data. Trackers are used to find other active computers, but do not store or share file data. Using the .torrent files, BitTorrent users can "Leech" (download) the files. Once a "Leecher" gets 100% of the file(s), they become a "Seeder" and helps "Seed" (upload) the files to other Leechers.
BitTorrent was the first client written for the protocol. Before version 6.0, BitTorrent was written in Python, and was free software. The source code for versions up to and including 3.4.2 were distributed under the MIT license and versions 4.x and 5.x were released under the BitTorrent Open Source License, a modified version of the Jabber Open Source License. Since version 6.0, BitTorrent is a rebranded version of µTorrent. As a result, its source is closed.
The BitTorrent protocol now has many clients, for example :