Without further ado, and in alphabetical order, some free apps that fit the bill: A curves adjustment tool lets you control color, color saturation, contrast, brightness, and black white points.
These features let you selectively apply edits and filters to portions of the image that you control. Can’t afford Photoshop? Can’t justify the expense? What do you need in a good photo editor anyway? To me, the absolute essential features necessary for any photo editing app are: