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.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
GIMP - GIMP is a multiplatform photo manipulation tool.
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
Microsoft Paint - Paint (formerly Paintbrush) is a simple, ultra-basic graphics painting program that is included...
Ralpha Image Resizer - High-speed image batch conversion tool