TorrentTrader provides a PHP-based Tracker application for the BitTorrent P2P protocol.
TorrentTrader allows anyone with a Web server supporting PHP and MySQL to run their own BitTorrent tracker. Also offered is a lite edition that does not require MySQL.
"It is an open-source project, which I have been in charge of from summer 2004 to summer 2005. Though I am no longer in charge of this project, you can find here for download the versions I have released."