Keywords
Pixelmator Pro is a super simple yet powerful image processing application for Mac. It has integration with Mac Photos and an app version for iOS (iPhone and iPad). Whilst it may not have as many features as some of the major commercial image processing tools, it more than makes up for it with ease of use and straightforward uncluttered menus and workflow. It also has a good user community and forums.
Pro: Price.
Pro: Ease of use and simplicity.
Pro: Nearly all that you need for most work without a thousand menus for things you mostly don't (Adobe, I'm looking at you).
Pro: Fine pixel level control and accuracy.
Pro: Super responsive such as quick in/out zooming.
Pro: The underlying image processing machinery is high quality.
Pro: Intelligent snapping is awesome (and nicely unified between image features, rulers, and selections).
Pro: Emphasises basic image editing and manipulation over silly so-called "AI" content creation.
Pro: Still uses the more honest "ML" to indicate machine learning features rather than suddenly sticking "AI" on every feature like some other image processing tools have (which features are mostly just basic image processing).
Con: Apparently no custom plugin support.
Con: The otherwise nice ruler system doesn't offer calculated distances between rulers. (Workaround is to use sized rectangles then hide them.)