Pixelmator is an easy to use alternative to Photoshop. Like Photoshop, Pixelmator is a layer-based image editor and as with Photoshop, you can blend layers, use masks and change their opacity.
It comes with the standard array of tools such as selection tools, painting tools and retouching tools. It also comes with an extensive set of filters, including Quartz Composer ones.
It handles over 100 different 100 file formats and can open and save Photoshop files with layers.
Available for the Mac, it has become a popular addition to many an artist’s toolset.
Cost: $59 from http://www.pixelmator.com/