GIMP is a cross-platform image editor available for GNU/Linux, OS X, Windows and more operating systems. It is free software, you can change its source code
Inkscape is professional quality vector graphics software which runs on Linux, Mac OS X and Windows desktop computers.
Paint.NETis free image and photo editing software for computers that run Windows.
DistroWatch is a website which provides news, popularity rankings, and other general information about various Linux distributions as well as other free software/open source Unix-like operating systems such as OpenSolaris, MINIX and BSD. It now contains information on several hundred distributions