Pixel Art Studio - A purpose-built drawing tool for pixel artists
Sketch - Professional digital design for Mac.
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Pixel Studio - The Pixel Art Is Always Fun
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.