Looks like the nice folks at Skylum (formerly Macphun Software) have made three of their apps free for macOS users.

Intensify “helps you create sharp, crisp and dramatic photos in 1 click.”

ColorStrokes lets you “pick a part of the image to leave in color and the rest of the photo will turn monochrome”.

My personal favourite of the three is Snapheal which often does a surprisingly good job of removing “unwanted objects & people from photos in 1 click”.