Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
AndreaMosaic - With AndreaMosaic you can create your own photographic mosaics made with your own pictures.
Pixel Art to CSS - Draw and animate pixel art, export the results to CSS
WidsMob Montage - Make stunning mosaic photos or montage shape with tiles, which supports both JPEG and PNG files.
Pixel Art Studio - A purpose-built drawing tool for pixel artists
Mosaic Creator - Mosaic Creator is professional mosaic tool. You can create your own picture mosaic.