Magica Voxel is a free voxel editor.
Qubicle is a paid voxel editor. It was used to create the art of the famous game Crossy Road.
Piskel is an open source software. You can use it online in the browser or offline on the PC.
Pixly is a pixel art editor for Android devices.
GraphicsGale Includes tools for animated sprites.
Hexels is a grid-based painting tool. In addition to using squares, you can use hexagons, triangles, and more.
A free tile map editor.
Paint of Persia transform any image or video into pixel art.