LightZone
[Macworld, Aug 9, 2007](http://www.macworld.com/article/1059212/lightzone3.html?page=0):
> If you long for simplicity in photo editing in an un-bloated piece of software, give LightZone 3.0.6 a try. Its unique visual approach to editing, time-saving Styles, and well-designed help system will aid the learning process. At the speed at which major enhancements are being released, I can’t wait to see version 4.
At the time of that writing, LightZone was a $200+ citizen of the photo editing elites, it has recently became [a freeware](http://lightzoneproject.org).
Darktable
That brings us to [Darktable](http://www.darktable.org), a “virtual lighttable and darkroom for photographers” whose user interface reminds me of Adobe Photoshop Lightroom.
[Mark Myerson wrote](http://mac.appstorm.net/reviews/graphics/darktable-the-free-lightroom-and-aperture-alternate/) a pretty comprehensive review of the app which I pretty much agree about.
I have yet to try LightZone, since it’s still [on beta for the Mac](http://lightzoneproject.org/node/348), but Darktable is available for the big three OSes.