What are some alternatives?
When comparing Krita and Paint.NET, you can also consider the following products
GIMP - GIMP is a multiplatform photo manipulation tool.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Pixelmator - Pixelmator is an image-editing application for Mac and iPad.
Clip Studio Paint - Powerful drawing and illustration tool.
Pixlr - Pixlr® makes it easy to transform everyday images into stunning works of art.