Pixopedia 2014 is an exceptionally powerful - but entirely free - image editor, drawing and painting tool.
The program doesn't create a particularly good first impression. Small flat buttons present various cryptic icons, there's no bundled help (you have to download a separate PDF, which is incomplete and outdated), no menus, and - you'll soon realise - no real interest in following Windows conventions.
Learn a few shortcuts, though, and life becomes much easier. Press [F1], for instance, and a menu appears for the currently-selected left toolbar option. By default this displays no less than 26 "Drawing Modes": Normal, Scaled, Erase, XOR, MinMax and many more. Clicking any of these displays its related options, and you can just click and drag on the screen to see its effect.
Exploring the left-hand toolbar (with the menu displayed) reveals many other interesting tools. You can "paint" with various clipart objects (bushes, flowers, butterflies, marbles, beads and more); apply 20 very configurable "warp modes" (Explode, Waves, Splash, Twirl); twist and shift colours; set various symmetrical drawing modes, and apply a host of useful filters.
Clicking the "Image Tools" button on the right gives access to a more basic set of image manipulations and tweaks: flip, mirror, rotate, resize, and various automatic enhancement tools.
Basic? Maybe, but the Plugins button and you'll find Pixopedia supports Photoshop-compatible filter plugins (*.8BF). And not only that, but it comes with 20 (mostly very good) examples from providers like Richard Rosenman, Mehdi, Redfield, Flaming Pear and Dragonfly.
And the feature list goes on with various selection modes, a range of shape drawing options, a configurable text tool, and what just might be the most configurable set of brushes we've ever seen in any free tool (or most commercial ones).
Pixopedia 2014 v0.3.0 changelog