I’ve been using Sleep as Android for many years now and it has not let me down. I highly recommend it. It is not open source, however.

I got one of these for free on a trashnothing Facebook group in my city. Someone was giving it away because it didn’t heat anymore. I popped it open and replaced the thermal diode. I’ve had to do that twice now. Great kettle for all types of teas and pour over coffee, but they should really make them more robust if they’re just expecting most people to toss it when a small inexpensive part goes bad.