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 Image Editor 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.
Doesn't have enough tools and has tools that shouldn't be paid, like layers.