WARNING this app sets your mac to default to opening every picture you have with it, even photoshop files WITHOUT ASKING. it can't open any archive formats like zip, cbr, cbz or rar and is more basic than you can believe. AVOID
Well you cant drag a folder of images on it. When I drag multiple images on it, each one opens in a separate window yet in any open window you can go back and forth to the other images. Not worth $3 and not ready for prime time. If you need a single image viewer just double click any image and Preview or Quick Look will do that.