#Mosquitto #mqtt is used nearly everywhere in the world. This is a map of installed locations for the snap package (which isn't even the most popular installation method). Used in 171 territories and only a very small amount of grey, where it is not used
Back in around February 2017, I created a self-serve service so people could generate client SSL certificates for #mqtt testing on test.mosquitto.org. It's generated 18881 certificates since then, or around 6-7 per day on average.