GIMP - GIMP is a multiplatform photo manipulation tool.
Piskel - Piskel is a website where designers online create sprites or pixel art.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
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.
Grafx2 - GrafX2 is a bitmap paint program inspired by the Amiga programs Deluxe Paint and Brilliance.