These are the projects that make use of TheTVDB's API. We encourage you to check them out.
XBMC is an award-winning free and open source (GPL) software media player and entertainment hub for digital media. XBMC is available for Linux, OSX, and Windows. Currently XBMC can be used to play almost all popular audio and video formats around. It was designed for network playback, so you can stream your multimedia from anywhere in the house or directly from the internet using practically any protocol available.
Plex/Nine is a flexible Media Center made up by two major components - the Plex Media Server and numerous Plex Clients. This lets you create a true server-based Media Center where information about all your media is stored in one single location. Plex/Nine also gathers information or metadata about your media and displays it in the Client making choosing which show to watch a rich and pleasant experience.
Sick Beard is a PVR for newsgroup users (with limited torrent support). It watches for new episodes of your favorite shows and when they are posted it downloads them, sorts and renames them, and optionally generates metadata for them.
Simple, dictionary-based Python library that allows easier interaction with TheTVDB's API.