GIMP is a freely distributed program for such tasks as photo retouching, image composition and image authoring. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, and more. Available also as portable app: http://portableapps.com/apps/graphics_pictures/gimp_portable
- GIMP is full of features that aren't needed by 99% of people and very complicated.
- Whereas Paint.NET is a very simple and user friendly program that's easy to use, GIMP is incredibly unforgiving, difficult to learn/use and lacking the welcoming and uncomplicated interface of Paint.NET. Moreover it has functions that just completely stop working for no reason
- Paint.net is a very easy to use program for basic editing of images, while Gimp is a very complicated tool for doing lots of complex stuff with images so kind of very different target groups I would say