Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Rasterbator - Wall art from any image
Sketch - Professional digital design for Mac.
Easy Poster Printer - Ever wanted to create your own poster?
Affinity Designer - Professional creative software, exclusively for Mac.
Block Posters - A free poster maker to create massive wall posters from your own images! Free!