Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Sculptura - 3D sculpting for everyone
Pixel Studio - The Pixel Art Is Always Fun
PaintCube - Web-based 3D painting software
Piskel - Piskel is a website where designers online create sprites or pixel art.
Nomad Sculpt - Nomad is a sculpting & painting mobile app, available on Android and iOS.