The Briar project is probably the most interesting project in this area. They recently released the first stable version [0] which includes bluetooth peer to peer messaging as a fallback if there is no internet connection available. WiFi peer to peer is also planned.

I would recommend listening to this presentation from ccc about the project: https://media.ccc.de/v/34c3-8937-briar

[0]https://briarproject.org/news/2018-1.0-released-new-funding....