What’s a Mac-Assed App?
The phrase "Mac-assed Mac app" is one I coined to describe apps whose design choices emphasize above all to be a Mac app. There's no one thing that makes an app Mac-assed. It's like what Paul Volker said about pornography: you know it when you see it.
Mac-Assed Mac Apps tend to be accessible. Often this comes from using standard controls and pattern, but not always.
Mac-Assed Mac apps tend to evolve with macOS changes with little extra work (usually).
They're probably not cross platform, but some might be. They might use standard widgets, or they might do something of their own. They're almost certainly not made with web technologies.