macOS Dashboard.
I loved it, back before it was removed in 10.15 Catalina; I had several post-its with stuff I wanted constantly on-hand, along with a few calculators and unit converters and stuff. It was great; sure, it couldn't do anything too advanced, and the stickies came in one-size-only (unlike the actual Stickies app), but the reason I preferred these widgets to the regular apps was that I could easily make them all appear/disappear by using a shortcut (move cursor to upper-right corner).
When Dashboard was removed, I stopped using stickies altogether as the Stickies app was just far too unmanageable in comparison, let alone the calculators and unit converters (I'd need to have the apps open all the time and manually switch to each window instance, or for Stickies have the constantly kept on top of other apps, when Dashboard had that easy shortcut as it was a different "Desktop" space).
Still annoyed it's gone, really; it was amazing. Should've removed Launchpad instead, as why use that thing when the Applications folder exists and you can search for apps using Spotlight? Launchpad is STILL utterly useless and worthless, yet the amazing Dashboard was trashed...