miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
Sketch - Professional digital design for Mac.
Paint XP for Windows 7 - Standalone old MS Paint program that allows you to get your old XP Paint interface in Windows 7.
Affinity Designer - Professional creative software, exclusively for Mac.