Mesh networking mobile chat apps?

Are there any modern mesh networking chat apps that can function without an Internet connection? Something that could work in a humanitarian crisis situation in the case mobile network is down.

I remember there was FirChat, used in Hong Kong protests in 2014, but I do not know if there is anything mesh-network capable today.

https://edition.cnn.com/2014/10/16/tech/mobile/tomorrow-tran...