Great option to other image editors and image creating software. It has a simple and intuitive user interface, yet supports both layers and 3D objects. Functional across all major OS. It is free, as in open source. It imports .PDN files created with Paint.NET without issues.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Dibuja - Gtk based basic paint program like MSPaint or Paintbrush but for Linux
GIMP - GIMP is a multiplatform photo manipulation tool.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
Microsoft Paint - Paint (formerly Paintbrush) is a simple, ultra-basic graphics painting program that is included...
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.