A friend mentioned this to me. It mirrors some features that Photoshop has. It's a nice little tool playing with it so far.
It's not going to replace your editor, but it is cool for something to work with quickly. Nice to have around as an option.
Similar in style to previously mentioned Aviary Phoenix, but without the 50-use limit, SUMO Paint is up-front about its similarities to a certain Adobe-made editor, giving you a floating toolbox, side-stacked palette and color bars, and menus with familiar options. If you're without your favorite desktop editor and in need of photo-tweaking power, SUMO can load images from uploads, URLs, and do its own in-browser copy and paste. SUMO Paint is free to use, no sign-up required.