GIMP is a free program for such photo retouching, image composition and image authoring. Essentially it's the closest thing to Photoshop you can get for free.
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 within concept art, texture and matte painters, illustrations and comics.
Paint.net is a free and very capable image editing software for Windows. Great alternative to Photoshop for people that do not need all the stuff PS offers.
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.
Paint (formerly Paintbrush) is a simple, ultra-basic graphics painting program that is included with almost all versions of Microsoft Windows. It opens and saves files as Windows bitmap (24-bit, 256 color, 16 color, and monochrome, all with the .
Glimpse is an open source image editor based on the GNU Image Manipulation Program. The goal is to experiment with new ideas and expand the use of free software.Discontinued
The Glimpse editor has been discontinuedSource: https://glimpse-editor.org/posts/a-project-on-hiatus/
PaintTool SAI is high quality and lightweight painting software, fully digitizer support, amazing anti-aliased paintings, provide easy and stable operation, this software make digital art more enjoyable and comfortable.
Enter a world of infinite creativity with the comprehensive photo-editing and graphic design power of PaintShop Pro X8. Accelerate your photo editing with enhanced layers, more precise selection tools, faster brushes and extensive productivity-boosting improvements.
A powerful and unique digital art program, focusing on natural media painting, photo editing and illustrative styles.
CinePaint is a deep paint application that edits EXR, DPX, 16-bit TIFF, JPEG, PNG and many other types of image files. CinePaint is available as a native application for Linux, Mac OS X, and BSD.This app doesn't have any features at the moment.Discontinued
The development is discountinued since 2013-05-06https://sourceforge.net/p/cinepaint/activity/?page=0&limit=100#599c65d15fcbc926952bcea9