Pyxel Edit is a pixel art and tileset creation tool. You can draw freeform like in any other graphics program, but you can also draw and place tiles. If you have multiple instances of a tile and edit one, they all update. It still works if some of the instances are flipped or rotated.

Some of its features:

• Tile references: draw in one tile and they all update instantly. This is handy when making tilesets because you can see how your tiles work together as a whole while editing them.
• Tile transformations: tile instances can be rotated and flipped, still referencing the same tile data.
• Tileset importing: Pyxel Edit can import images of tilesets or mockups and identify all the unique tiles automatically, allowing you to edit and rearrange old tilesets or doing edits of mockups easily.
• Tilemap exporting: export your canvas tilemap in XML or plain text format for super quick game prototyping.