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.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
MS Paint IDE - The most partially downloaded IDE on the internet