Photopainter is described as 'is both a natural-media painting software and an image processing system at the same time' and is an app in the Photos & Graphics category. There are more than 100 alternatives to Photopainter for a variety of platforms, including Windows, Mac, Android, iPhone and iPad. The best alternative is GIMP, which is both free and Open Source. Other great apps like Photopainter are Krita (Free, Open Source), Adobe Photoshop (Paid), Paint.NET (Free Personal) and MyPaint (Free, Open Source).
Krita is a professional Free and open source (FOSS) painting program. It is made by artists that want to see affordable art tools for everyone withith concept art, texture and matte painters, illustrations and comics.
MyPaint is a fast painting program with an emphasis on full-screen use. It lets you focus on the art instead of the program. You work on your canvas with minimum distractions, bringing up the interface only when you need it.
Pixlr® makes it easy to transform everyday images into stunning works of art. Whether you’re applying a quick fix to your photos or adding your personal touch with effects, overlays, or borders, Pixlr has everything you need to make your moments beautiful.
Pixelmator is a powerful, beautiful, and easy to use image editor. Featuring an elegant and streamlined single-window interface, it puts all the focus on the images you edit, rather than what's around them.