Paint.NET is described as 'Free image editor for Windows, offering layer support, plugins, special effects, and portable use without installation. Lightweight and ad-free' and is a leading digital painting tool in the photos & graphics category. There are more than 100 alternatives to Paint.NET for a variety of platforms, including Windows, Mac, Web-based, Linux and iPhone apps. The best Paint.NET alternative is Pinta, which is both free and Open Source. Other great apps like Paint.NET are Krita, GIMP, Adobe Photoshop and Pixelmator.
This is for Processing images, not for editing them.