Good opentherm gateway
For OpenTherm Gateway Arduino Shield
Product works as described, clean board with good indications and general documentation. My recommendation is to buy the kit, soldering SMD is tricky without experience and an error is too easy to make with possible dire results for the board (happened to me, not the fault of the author).
Software library was easy to adapt to my ESP32 (support will most likely be incorporated into next release). Responsive and helpful owner.
Documentation for testing needs extensions for 3.3 Volt case, most likely will be addressed after my feedback.