Lightroom alternative?

I quite like F-Spot + UFRAW for organising photos and processing them but I also use Darktable for when I get bored of UFRAW.

I use Darktable too. If your camera is supported RawTherapee will be an option as well.

I have been quite happy with using Bibble 5.

While it is a commercial program, I find it outstrips all open-source solutions in both usability and speed - at least for my uses. And they have quite good Linux support, including .deb-packages and simultaneous releases on all platforms.