Trigraphy - Photo editing app that allows you to make mosaic/abstract looking art.
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
GIF Brewery by Gfycat - Create stunning GIFs from videos & screen recording for free
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
WidsMob Montage - Make stunning mosaic photos or montage shape with tiles, which supports both JPEG and PNG files.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.