I’ll answer this a little differently by saying that I view the macOS ecosystem as being my primary productivity tool. Many apps in this list have already been mentioned, but it would be remiss not to mention that a good proportion of them are available via SetApp for a low-cost monthly subscription.
There are a number of factors that make macOS the best choice for productivity, but two of the main ones are that macOS sits atop a UNIX underbelly and secondly Apple make available a huge number of frameworks that independent developers can build upon to make great apps that excel in highly targeted use cases.
In many ways, the apps I list below build upon the UNIX design strategy itself, of providing many focused routines to solve very specific things; routines such as grep, sed and awk for text manipulations.
Keyboard Maestro is awesome, but much of what makes it great is its ability to lean on shell scripts, and of course AppleScripts. As @korm mentions, macOS Services are a great way to lean into the power of shell scripts, even if you have no familiarity of the command-line. The macOS services provided by Devon Technologies provide many of the same text processing capabilities as TextSoap or the Text Factories in BBEdit.
Another critical factor of macOS itself being the ‘edges’ on the productivity ‘graph’ for its users, is the fact that many such utilities can be running in the background with minimal processing/memory overhead. That way, they’re waiting to be called at the point of need, and then get out of the way, with similar elegant aplomb.
The monolithic software development processes of old has meant some of these essential apps suffer with a long history of feature creep - peripheral features added to justify upgrade sales. But there’s nothing stopping you from sticking to the core features that made those apps great in the first place.
So, my list, in no specific order, includes.
Default Folder X
TextSoap
Keyboard Maestro
Cloud Storage (pick your flavour)
Droplr
Yoink
Dropzone
PopClip
Tot
Antinote
Obsidian
Typora
Floating
PureRef
Hookmark
TextExpander
Alfred
SimpleMind
OmniGroup Apps (primarily OmniOutliner, OmniFocus and OmniGraffle
BetterTouchTool
OpenIn
Hazel
Swish
HazeOver
Curio (strictly as a whiteboard for creative exploration)
BBEdit
Dash
CodeRunner
VS Code
Scrivener
Ulysses
Skim
Calibre
Kindle
Acorn
Retrobatch
PixelMator Pro
GraphicConverter
If you’ve made it this far, I’ll call out a few applications of particular note. I work in the creative sector, so subscribe to the full Adobe suite, however I still find a place for Acorn, Retrobatch, PixelMator Pro and GraphicConverter and that’s because each have strengths when called via Shortcuts or Applescript. And Keyboard Maestro makes it possible to combine these AppleScripts into powerful standalone macros.
Another pair worth singling out are Tot and Antinote. On the surface of things, they each do the same thing, and that’s to provide standalone scratch-pad notes for temporary scribblings. Tot is essential as it has both macOS and iOS apps, which sync via iCloud. Antinote is a €5 pay once delight, which is only available on macOS, but its worth having as it leans into shell-scripting behind the scenes to provide a bunch of clever features which come in very handy in short-term temporary plain text scratch notes. Further info here: Antinote: Beautiful Temporary Notes and Calculations