Interesting replies but I’m just wondering what file format to use.

ascii + markdown for text if you’re from the US

Don’t we have troubles opening stuff from 4-5 os versions ago?

Yeah, but that is because people want to make money and so make their file formats difficult to understand on purpose.

Whatever creatures discover our mystical tablets will hopefully be far smarter than us, or they’ll use the sum of human knowledge to tile their bathrooms.