Inspired by this Mastodon account, I programmed an ESP8266 microcontroller to act as a traffic light, indicating the current electricity mix. Check it out on Codeberg! It uses an API from the Fraunhofer Institute and the parts cost around 5€. In my shared flat we use it as an indicator on when to run demanding devices, like the washing machine.
By saying that it cost around 5€ I meant that the material to build this cost me around 5€. I would happily set them up for free if one gave me the material for free, but the microcontroller and so on do cost some money.
The API and (of course) the source code are free (as in freedom, being AGPL licensed). And since I did my best to document it well and provide easy to follow instructions in the README, I do think I managed to make it free as in freedom.
Oh, sorry, didn’t understand it like that 😁… thought that was the price of the license for the library 😁.
Of course, the parts come at a price, no surprise there 😂.