haven’t tried it yet, some limits on camera compatibility, but it is a well reviewed (and not new) competitor in the wake of Adobe’s recent announcements…
http://petapixel.com/2013/07/09/lightzone-photo-editing-software-is-now-open-source-and-completely-free/?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+PetaPixel+%28PetaPixel%29