Gimp:

Gimp is a free and open raster graphics editing program. It allows retouching, editing and conversion between different image formats. It is available for all common platforms.

It offers all basic image processing functions as well as some advanced functions such as layers, masks and channels. Automation of image editing and processing is also relatively simple. All common image formats are supported, including the proprietary PSD format.

Adobe Photoshop:

Photoshop, developed and distributed by Adobe, is the most widely used image processing program in the semi-professional and professional sector. It offers a variety of possible image manipulation tools and also supports most image formats. Internally Photoshop stores images as PSD which is also compatible with other Adobe software. Adobe Photoshop is available for Microsoft Windows and Apple MacOS

Inkscape:

Inkscape is a free and open vector graphics editing program. It can be used to create, edit and convert vector graphics such as illustrations, diagrams, drawings and logos. The primary format used by Inkscape is SVG, but many other formats are supported. Inkscape is available for Microsoft Windows, Linux, macOS and FreeBSD.

Adobe Illustrator:

Adobe Illustartor is the vector graphics companion to Adobe Photoshop. It is also very common and offers a variety of advanced features. Internally, Illustrator uses its own proprietary format, but other formats are also supported. Adobe Illustrator is available for Microsoft Windows and Apple MacOS.

IrfanView:

IrfanView is primarily an image viewing program. However, it is possible to perform simple image manipulations and conversions. Non-commercial use is free of charge. All common raster graphics can be displayed and converted. IrfanView is only available for MIcrosoft Windows