Enthread is a web based image editor that has some easy to use, simple editing features. Simply drag your image to the center of the page and get started.

Adjustments include: Hue/Saturation/Lightness, Brightness and Contrast, Colors (RGB), Filters (sharpen and blur), and Process (Sepia, Desaturate, Solarize, Invert, and Edges). You can undo any edit you make, as well as save and share the finished product.

That is literally it. Easy to use, online, and simple. Great for basic edits and adjustments.

Related:

Great, free Image editing sites and software

Two More Free Image Editing Resources

PicMonkey - free online photo editing