Once Elon evolves X to the everything app, we will finally enjoy what is what you describe and what is already the case in China.
I was there a month ago and we were driving through some rural area and the bus stopped so people can go to the toilet. There was a seller selling dried fruits in small plastic bags. I wanted to buy some and I had some cash on me, but the only way to pay was to use WeeChat and the QR code he had there.
I use radicals for CalDAV and save notes there together with my calendars. On Android there is jtx Board which let’s you work with them. Sadly on Linux I couldn’t find anything so I started writing something myself but don’t have much time to work on it https://github.com/jeena/JNotes