(the link again in case the clickable title doesn’t work on all instances: https://sketchtoy.com)
Have you ever tried to explain something over the internet that doesn’t translate well into words (like a specific route on a map, the layout of a building etc.) and you also can’t find a good picture on the internet showing what exactly you mean? Then just use that site to doodle a sketch. It is free of charge, doesn’t require a registration/verification/whatever or extra software, and the sketches seem to stay online forever.
I have an online roleplaying group that relies solely on chat / texts and this site has helped me numerous times to demonstrate the layout of a tavern, camp or dungeon, to show what in-game items look like and/or how big they are, and to add easy-to-understand visuals to in-game puzzles that would otherwise be hard to describe verbally.
Paper. You can use paper and take a picture with your phone.
Hmm does this Pa-per record my usage, or harvest data from the room I use it in? What about the EULA for Pa-per, you know, in case I want to understand all the ways I’m being taken advantage of, but listed in the hardest to consume way possible?