FOSS IoT Devices?

Does anyone have recommendations for IoT outlet switches, power meters, temperature/humidity sensors, etc. that have a fully free and open API? I'd like devices that I can just hit over a simple HTTP API over the local network with no cloud integration whatsoever. I want to make these devices scriptable for hobby projects that I can run off the local home server.

I've spent so many hours searching, but all the available consumer options either have proprietary closed APIs, or can only be used through cloud Google Home/Amazon Alexa/etc which I explicitly do not want. (Someone reverse engineered the API of a TP Link device, but I this sounds like a maintenance burden if they ever push a cloud OTA update that nukes this backdoor.)