Krita

Crescent is primarily an application on digital drawing, although it can be used as an image editor, or even used as a vector graphics tool. Initially, it was made for Linux as part of the Kdea and was included in the Kolligara Suite. This version provides all the features of the original application, but now for Mac environments.

Interface styles are influenced by Adobe products, as well as by Corel Digital Drawing Tools, so those who used Photoshop before they hang quickly.

It has support for various types of brushes and effects, the ability to work with layers, the most used image format, palette, crop, and vector manipulation, and various relieving tools.

The best thing about it, though, is that it is an open source application under the GNU license. This makes it a great alternative for a gimp, it is by far the most popular open source image editor.