Draktable 2 is available. Download it for free! Darktable is an open source dam/raw editor. Best part is you can use External Editors for Photos extension to use Darktable. I use Darktable for frequency domain editing and it is simply the best tool for frequency domain editting. However, you'll have to export a tiff back out and drag it into Photos. i haven't figured how to get it to export a jpg back into in Photos after i'm done.

http://www.darktable.org/install/#osx