Pixelate your dreams! - github / Showcase

Doc

• Pixelorama – Great Free Pixel Art & Animation Tool with a Twist! - show basic usage + internals
• can import palette from image eg from pico8
  • but does not support (yet) indexed palette

see also:

• LibreSprite - a fork of Aseprite
• Piskel
• bobsprite.com
• pixilart.com