BitTorrent is a peer-to-peer program developed by Bram Cohen and BitTorrent, Inc. used for uploading and downloading files via the BitTorrent protocol. BitTorrent was the first client written for the protocol.
BitTorrent is often nicknamed Mainline by developers denoting its official origins. Version 4.20 of the client was dubbed Allegro by BitTorrent Inc., in reference to protocol extensions developed by the company to accelerate download performance and ISP manageability.
Since version 6.0, the BitTorrent client is a rebranded version of µTorrent. As a result, its source is closed, and this version of the program is currently only available for Windows (although, like µTorrent, the FAQ suggests to use it in Wine).
Prior to version 6.0, BitTorrent was written in Python, and was free software. The source code for versions 4.x and 5.x are released under the BitTorrent Open Source License, a modified version of the Jabber Open Source License. Versions up to and including 3.4.2 were distributed under the MIT license.
