GIMP - GIMP is a multiplatform photo manipulation tool.
Epic Pen - A windows tool for drawing over your desktop and applications
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
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.
PaintTool SAI - Learn to draw in different ways.
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.