I'm familiar—as I'm sure many are—with the big names: BBEdit, Fantastical, Transmission, etc. I want to hear about great, lesser-known Mac apps, and about the design elements that made them so great.
It's fine if the app is no longer actively supported. At a time when the Mac platform seems to be shifting direction, I'm as interested in old apps as new ones.
(I suspect someone will ask what "Mac-Native" means, and I'm not particularly eager to weigh into that discussion. The apps do not need to be Mac exclusive, but they should feel highly tuned to the platform. No electron!)
https://rogueamoeba.com
Reeder 2. The one thing it had that other RSS apps didn't have is collapsable columns. Accounts was the leftmost column. When you selected an account, it would collapse to the width of a small icon. The next column is the RSS feeds, which would do the same after you selected a feed. This left only the list of news items and the viewer taking up most of the space. Screen real estate is less of an issue in this day and age of 4k screens, so they removed this particular feature, but I always appreciated it.
DaisyDisk. Again, nothing clever, just a beautiful interface that always works and always does what you expect it to. I wish it was a little faster, like WizTree, but that might have more to do with HFS+ than the app itself.
https://daisydiskapp.com
Quicksilver. It's mostly been replaced by Alfred at this point, but there were things you could do with Quicksilver that you can't do with Alfred, such as chaining files, actions and apps together on the fly. I think you can do something similar in Alfred with Workflows, but you have to set it up ahead of time. Quicksilver had a set of built in actions that would let you do a surprising number of things on the fly, like open an application in AppZapper.
https://qsapp.com
AppZapper. I don't know if this one qualifies as a "big name" or not, but it's always the first app I install on a new Mac.
https://www.appzapper.com