Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Trigraphy - Photo editing app that allows you to make mosaic/abstract looking art.
Sketch - Professional digital design for Mac.
Dreamscope - Make and share 'deep dream' images using dozens of supplied styles or your own.
Affinity Designer - Professional creative software, exclusively for Mac.
Photomosh - Turn anything into a vaporwave