vvvP: http://vvvp.sourceforge.net/ Open source. Linux, Mac and Windows.

vvvP is open source and it works under Linux, Mac and Windows. You can even share your catalog from a network server. It catalogs images and it stores thumbnails, you can add descriptions and create a hierarchy of virtual folders to organize the images. It supports RAW images. http://vvvp.sourceforge.net/

This is a young program designed to catalog photographs: http://vvvp.sourceforge.net/ Linux, OS X and Windows. It stores everything in a single file so it is easy to backup. It does not store tags in the image itself, but this will be added in future versions.