The Arduino sketch and WordPress plugin are linked on the site, those are on github.

The rest is a flask site I made to register people on the mosquitto mqtt service that I set up on my server - that will eventually be open sourced as well though - I'm concentrating on getting people to test it first.

If you are just doing it for yourself there are a ton of free services, like Adafruit for example. The mosquitto setup was a bit of a mission!