I have not, yet. But I would definitely consider making one. It's a very interesting tool, particularly for those with less reliable internet connections. Think of it as turning phones into relays that store notes but also share them with other nearby phones via bluetooth.

When they say 'sending notes offline', the one phone is offline but connecting to another phone that is online via bluetooth? Why? What is the use case?

You can find here some examples:

GitHub

GitHub - KoalaSat/samiz: BLE mesh for nostr notes when the internet is down

BLE mesh for nostr notes when the internet is down - KoalaSat/samiz

You can find here a quick example:

So at a conference I could be posting on Nostr via bluetooth. Maybe next year bitcoin Prague?

You can start testing it out now 😄