GIMP

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.

Free Open Source Mac Windows Linux BSD Snapcraft ... FLATHUB PortableApps.com Haiku AmigaOS

Paint.NET

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.

Freemium $ $ $ Windows Windows S .NET Framework

MyPaint

MyPaint is a fast, distraction-free, and easy painting tool for digital artists. It supports graphics tablets made by Wacom, and many similar devices.

Free Open Source Mac Windows Linux PortableApps.com

Pixlr

Pixlr® makes it easy to transform everyday images into stunning works of art. Make every moment beautiful with our family of photo editing apps.

Freemium Web Android iPhone

Pixelmator

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...

Commercial $ $ $ Mac iPhone iPad

Microsoft Paint

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...

• Discontinued
  Microsoft announced that Paint is officially deprecated with the Windows 10 Fall Creators Update. Anyway last version of the program will still be usable in Windows 10.

Free Windows

Glimpse Image Editor

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.

Free Open Source Windows Linux

Leonardo

We believe artists deserve the best possible tools and we are determined to give it to them. The goal with Leonardo is to make the best painting application ever.

Commercial $ $ $ Windows Windows S

Pixelesque

Pixelsque's goal is to be as simple as possible, while still retaining many powerful features. It works like any standard pixel art editor, with a pen, eraser, and...

Free Open Source Android Android Tablet

JugiPaint

JugiPaint is a painting software with diverse sets of tools for various types of illustration work. It provides many standard digital painting features like layers...

Commercial Windows