GIMP

When it comes to editing photos, you can either get an expensive editor, which can satisfy all your needs or you can opt for a free one, which doesn't come with too many features. GIMP offers the advantages of both solutions and the drawbacks of none. It comes with a huge amount of editing tools, which you would expect to find in advanced editing programs, like Photoshop. What's more, the software is offered completely free of charge and it can be used on all major platforms, including Mac OS X.

GIMP's user interface is composed of a main editing window and two floating panels, which can be moved independently anywhere on the screen. Once you load a picture or create a blank canvas, you can start using a wide range of basic editing tools, like brushes, stamps, blur, sharpen or burn tools, cutters or a magic wand and others, which can be found on one of the aforementioned panels. In the second panel you can find the loaded image's histogram, created layers, color channels and other utilities.

Besides using the editing tools on the floating panels, you can also look through the menus, on the top edge of the screen, to find a wide selection of advanced features, like filters, color balance controls, levels and curves adjustment options and much more. The available filters are neatly categorized in sub-menus. Some of them are applied instantly, without any further user input, while others require additional tweaks, on separate windows.

Just like other advanced editors, GIMP is quite flexible when it comes to layers. Besides simple layers, you can also create layer groups, masks, alpha channels, create layers from selections, duplicate or merge them and so on. In other words, the program gives you complete freedom to manipulate your pictures and create new effects however you want.