I love PCalc. It's not "simple" by default, but you can make it into what you want.

I've used PCalc for years (I'm pretty sure that I started using it when MacOS 9 was still the main operating system).

It also works for iOS and WatchOS.

Love Calca on iOS.

http://calca.io/

Adore Calca on macOS and windows.

Try this for simplicity: https://apps.apple.com/app/grandma-calculator/id1546631829

It doesn't get more $2 Casio than that.

There's a port of the Windows calculator on the Uno Platform that's ad free, although not paid. https://github.com/unoplatform/calculator

I like Tydlig

I love Tydlig