Ant Movie Catalog is a free, open-source program made to manage your collection of movies on DVD, CD (VideoCD, DivX, ...) and tapes.
If you use GNU/Linux rather than Windows, you can try to use WinE to get this program running; some people notified me that this was working. You can also check Moviefly, which is a complete rewrite of Ant Movie Catalog made with Python.
If you're looking for a program to catalog other things such as books, audio CDs or games, check the "Mods" section of the forum where you'll find modified versions of Ant Movie Catalog. For games, a new program derived from Ant Movie Catalog has been made: Sisimizi Game Catalog.
It just works, and it's not pulling data from a proprietary database.
Wish the developer would concentrate more on design. The app is just plain ugly.