Aseprite
Animated sprite editor & pixel art tool
...Support for color profiles and different color modes: RGBA, Indexed (palettes up to 256 colors), Grayscale. Animation facilities, with real-time preview and onion skinning. Copy & paste. Drag & drop. Resize palette. Palette entries with alpha value. Select color harmonies. Create light and shadows with the shading ink. Create perfect strokes for pixel-art. Avoid extreme pixel distortions when rotating tiny sprites. Create patterns repeating the image in a 3x3 grid. Create custom brushes for dithering. Composite layers to create color effects. ...