I just discovered MaxCurve and it's totally awesome!!!! Curve tool for RGB and LAB colorspace!!!! also has has interesting curves for contrast, exposure, gamma, temperature, lightness, and B&W. It also has an interesting HSL curve tool!!!! also has extensions!!!!
If you are a curve freak like me, you must get this!!!! it's totally awesome.
MaxCurve - Curve tool & image editor for pro photography by Xiaodong Wang