I use the M5Stack C124 AtomS3 Lite with the RS485 Base for direct local control of my Rheem water heater. (I have the heat pump version, but it works with other versions also)
https://github.com/esphome-econet/esphome-econet
Way better than using the econet integration in home assistant. It eliminates the need for the Econet account and cloud. Now it is all local and provides way more information and options than the built in integration.
I know it isn't technically a stand alone project made by a specific company, but it was so easy to install and setup and really pretty cheap. No soldering and just some very minor modifications to an existing phone cable that I sacrificed to the cause.