phpMyBitTorrent: BitTorrent Tracker written in PHP. Features include: hosting torrents from remote trackers, DHT, Compact Announce, alternate links (eD2K, Magnet), HTTP-Basic Authentication, Passkey Authentication, embedded HTML Editor, Mass-upload of to
Aria2Web is a PHP- and Javascript-based application that allows you to control the excellent and lightweight "aria2" over the web. That way you can use it as a download manager.
ajaxTorrentUI is a FREE PHP and AJAX (Javascript) based BitTorrent client. Manage all of your Torrent downloads through a desktop-like interface from anywhere. Requires Apache with PHP and BitTornado source (included).