Project is licenced GPLv3, but requires a CLA, which asks for an exclusive licence. It then seems to grant you a licence back though, but wat? I asked in their discord about it, and got an unfriendly feeling response. They didn't seem keen to discus it further. My impression is they plan to pull a commercial privatisation on the project and profit from free labour, otherwise why the CLA?

Why you probably shouldn’t add a CLA to your open source project

Map of nodes made from data on pubic MQTT server