Quietnet

[proxx]

Also neat:

https://github.com/Katee/quietnet

Simple chat program using near ultrasonic frequencies. Works without Wifi or Bluetooth and won't show up in a pcap.

Note: If you can clearly hear the send script working then your speakers may not be high quality enough to produce sounds in the near ultrasonic range.

[Kulverstukas]

This is cool, however both receiver and sender must be close to each other

[proxx]

This is cool, however both receiver and sender must be close to each other

That is what I was thinking
These are the kinda ideas that drive me to code, there is much still to do and invent , creation drives me.