A lot of people metion "Reticulum" in this regard. But that's a one-man-show project.

The only project that got some serious momentum is Meshtastic. That's decentralized LoRa with flooding/next-hop-routing that can be backed with MQTT.

I think a huge step forward would be a decentralized BLE LE (a super robust Bluetooth Low Energy mode) Mesh based application as it can be used on smartphones.