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.
Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Windows and macOS. It was originally created in 1988 by Thomas and John Knoll.
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.
RawTherapee is a free RAW converter and digital photo processing software. All changes can be applied and batch processed at a convenient time.
PhotoScape is a fun and easy photo editing software that enables you to fix and enhance photos.
Photoscape vs Sagelight opinions
Sagelight appears to be no more. Photoscape runs as a Windows 10 app.
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/
From high-precision light and color tools, to advanced clarity and dehaze settings, to the ability to create and save your own filters. Polarr is the ideal photo editor for bloggers, students, and photo professionals alike.
FireAlpaca is the image editor that can be used readily and easily. We made it possible to provide the completely free download, in order for our products to be experienced by more users from all over the world. It is available for both Mac and Windows users!
PhotoFiltre 7 is a complete image retouching program. It allows you to do simple or advanced adjustments to an image and apply a vast range of filters on it. It is simple and intuitive to use, and has an easy learning curve.
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.