Darktable is a photo editor for Linux that is really quite impressive. Darktable describes itself as an open source photography workflow application and RAW developer.
Darktable offers basic image, tone image, and color image operations. It also offers correction models and effects / artistic post processing. Or put another way, Darktable offers a comphrensive photo editing solution with some pretty cool tools.
A lot of folks complain that there is no Lightroom like photo editing on Chrome OS. I am not a big fan of stating this app on Linux is like or can replace that app on Windows or Apple. With that said, I was very impressed with Darktable and it certainly is an application directed towards users anywhere from amateurs to professionals.
Darktable can be installed on any unix based operating system such as Linux, Unix, or Mac OS. While there is technically nor port for Windows, the developers offer an interesting work around. You can also join a Darktable community on Google +.