Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
Grafx2 - GrafX2 is a bitmap paint program inspired by the Amiga programs Deluxe Paint and Brilliance.
GIMP - GIMP is a multiplatform photo manipulation tool.
Piskel - Piskel is a website where designers online create sprites or pixel art.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.