Device-to-device audio communication (think QR codes, but made out of sound) seems very underrated. Much better UX than QR codes or NFC because you don't have to worry about putting your phone in the exactly right place or pointing it in the right direction.

Anyone here with more detailed takes on this?

We built this for payments in India on low-end devices, enabling peer-to-peer and merchant payments. App was initially called Tez and is now called Google Pay India.

It works!

We built this for payments in India on low-end devices, enabling peer-to-peer and merchant payments. App was initially called Tez and is now called Google Pay India.

It works!

https://www.theverge.com/2017/9/18/16325004/tez-google-india-audio-qr-cash-payments

Perhaps this is what @vbuterin was referring to in this cast:

Perhaps this is what @vitalik.eth was referring to in this cast:
https://warpcast.com/vbuterin/0xd2f95f