Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
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.
Pixel Studio - The Pixel Art Is Always Fun
Clip Studio Paint - The artist's software for drawing and painting.
Pixel Art to CSS - Draw and animate pixel art, export the results to CSS
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.