GCstar is a free open source application for managing your collections which works on Linux, Windows and Mac OS X. Detailed information on each item can be automatically retrieved from the internet and you can store additional data, such as the location or who you've lent it to. You may also search and filter your collection by many criteria.
The current collections supported by GCStar are: movies, books, music, wine, board games, comics, numismatic (coins), TV shows (episodes) and video games but you can always create your own collection type. Also, GCstar can import collections from different collection managers such as Alexandria, Ant Movie Catalog, DVDProfiler, GCFilms, MyMovies and Tellico.
GCstar has an GTK, KDE and base skin, so it should look ok on both KDE and Gnome. It it also fully or partly translated in these languages: Arabic, Bulgarian, Catalan, Czech, Dutch, English, French, Galician, German, Greek, Hungarian, Indonesian, Italian, Polish, Portuguese, Romanian, Russian, Serbian, Spanish, Swedish, Turkish, Ukrainian.
To see GCstar in action, I've just recorded a small screen-cast:
