[watersb]

PCalc -- because it runs on every Apple platform since the Mac Classic:

https://pcalc.com/mac/thirty.html

My other favorite calculator is free42, or its larger display version plus42

https://thomasokken.com/plus42/

For a CAS tool on a pocket mobile device, I haven't found anything better than MathStudio (formerly SpaceTime):

https://mathstud.io

You can run that in your web browser, but they maintain a mobile app version. It's like a self-hosted Wolfram Alpha.

[Melatonic]

The last one was interesting but both apps haven't been updated in 4 years. Hard to pay for something like that.

They do have some new AI math app that's regularly updated