GIMP

GNU Image Manipulation Program, also know as GIMP, is a free and open source multi-platform photo editor. It is one of the most sophisticated open-source photo editing tools, commonly used as an alternative to programs like Photoshop - which it can read the files of!

Wilbur, the mascot for GIMP. This is the logo for GIMP as of 3.0.

Usage

GIMP is a very sophisticated photo editor for its class. It has layer support, plugins, many brushes, and a whole lot more.

GIMP uses the .xcf format to store project files. However, it also can open Photoshop (*.PSD) files.