GIMP is a free and open-source raster graphics editor used for image manipulation and image editing, free-form drawing, transcoding between different image file formats, and more specialized tasks. GIMP is released under GPL-3.0-or-later license and is available for Linux, macOS, and Microsoft Windows.
Similar to PhotoShop GIMP is a very powerful tool for editing images but just like Photoshop it takes many hours of study to learn its intricacies.