This tool gives you all of the basic functions necessary to tweak an image to your liking, and it lets you add effects and other improvements.
Then, you can blur, reverse colors, distort, darken, adjust light, contrast, and saturation, and basically make any type of fix you want.
In addition to the different options for directly tweaking the image, you can also change the image's size, rotate or invert it, and even superimpose text onto it.
If you're looking for a simple and comprehensive image editor, Splashup Light is the tool you were waiting for.
Requires you to install the Adobe AIR app.