Webapps have few limitiations these days. Nothing exemplifies this change better than photo editing tools, and online editor Fotor collates a handy collection of basic image tweaking tools.
Fotor includes many options that will be famiiar to Photoshop users. I was pleased to see Curves for more complex editing, but if you prefer something less complex you also have access to tone, sharpness, brightness and other slides for super-easy adjustments.
For those looking for more than simple colour correction, filters and frames can add a variety of effects. You can also add image stamps and text if you like. Most impressively, Fotor handles HDR processing for you. If you took a bunch of images to create a composite HDR image but don't have the software to handle it, just upload them to Fotor and now you can work with them effectively.
Overall, Fotor handles most photo editing tasks you'll need. You can check it out online for free, without even signing up.