Managing digital photographs has always been fundamental requirement of photographers - Professionals and Amateurs alike. While amateurs (or hobbyists) like myself who use Windows make do with tools combinations like Picassa + The app that came with your camera, etc. But with Mac users, Aperture continues to be one of the most popular choices.
But the open source Ubuntu Linux has a few good choices too. Here's an article by a Mac user who tried to search for Aperture-like features on Ubuntu and was impressed.