Tools I'm surprised aren't better known:
- http://Libgen.is  — free books! (don't forget to buy the ones you like)
- http://photopea.com  a Photoshop clone that runs in the browser. 99% of the features, exact same UI and keyboard shortcuts, 100% free

- KillSticky: a Chrome extension that hides all sticky elements when you press Cmd+K. Great to unclutter a page / remove the headers and footers preventing you from paginating using the space bar
- http://Remove.bg : just drag and drop an image to remove its background

- http://Raindrop.io : my favorite bookmark manager (once you start using one, you wonder how you used to live without it)
- KeyboardMaestro — just search for my mentions of it https://twitter.com/search?q=from%3A%40altimor%20keyboardmaestro&src=typed_query

- Alfred: like Spotlight, but better. The clipboard manager feature alone makes it a killer app. And same here — once you start using one, you can never go back.

(My usage of Alfred: 15.5k times since 2017, or 13.4 times a day. At $29, that's $0.002 per use.)

- Contexts: fixes MacOS Cmd+Tab, making it behave like Windows' Alt+Tab, which is how God intended window management to work https://contexts.co/