Note (Oct 2023): The names of the buttons have been changed again in the SDK in macOS Sonoma - I will update the blog post again once I have Sonoma on one of my Macs :)
Back in October 2014 I wrote a post about different styles of NSButtons.
That was in the era of OS X Yosemite and Xcode 6. I started researching what each kind of button available in Interface Builder was for, because I couldn’t figure that out from Xcode and the built-in documentation - I dug a bit into the Human Interface Guidelines, some older documentation archives and into Apple apps themselves. I collected everything into a long post that went through all the button styles and described what I could find about each one.
It seems that a lot of people also had the same problem, because the post turned out to be extremely popular. It’s around #3 in total page views on this blog, and 7 years and 7 major macOS versions later it still usually comes out #2 in monthly or yearly stats and still gets a couple hundred visits a month. Even with greatly improved documentation in Xcode and much expanded content in the modern HIG, there’s clearly demand for this kind of information collected in one place.