I just installed it on Linux. It is curves on steroids as pphuang said. That function is called Zone Mapping. It also has Tone Mapping, and I'm not quit sure what it does, yet. The masking tools are really very good, you can visually see the feathering area and you can adjust it on the image. It seem much easier to use than the PS tools for masking. It then has all the PS stuff like sharpening, blur, histogram, white balance, white point, color temp, and on and on. It is well thought out, better than PS. For instance, when masking, hiding the mask is easy, and inverting the masked area is easy. I like the quick way you can mask an area adjust then mask another area and adjust, if you don't like something as with levels you can go back to it and change it. Overall I like it but I still need a few filters like borders or the healing tool. I also handles RAW files.