Firmware for my meteo (historically) devices, which have temperature, humidity, co2, power spent, water spent sensors connected. About 10 devices are online in 4 different locations. First device with this firmware created in 2018.
Data is sent to my server and viewed by Grafana dashboards. Public dashboard with outside temperature available here: Grafana
Typical device based on esp8266 chip (kind of Arduino with WiFi) and looks like this.
My favorite part is that all devices have identical firmware and load its configuration on start based on chipId (at beginning of project I maintain different firmware for every device and it was a lot of headache 🤯).