GIMP - GIMP is a multiplatform photo manipulation tool.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Pixlr - Pixlr® makes it easy to transform everyday images into stunning works of art.
Fotor - Fotor is an all in one visual platform. It includes photo editor, collage maker, and graphic designer. You are free to make a visual look more beautiful.