Funny that it's been forgotten a bit, but the Sensebender was official hardware of Mysensors. https://www.mysensors.org/hardware/sensebender-gateway
The official source was through itead, and it's actually still available to order, which really surprised me! https://itead.cc/product/mysensors-gateway/
It worked well when I used it, but whenever I had another idea of something I wanted to build, I kept running into problems with mysensors, and had to rework things. I finally ended up giving up and going with ESPHome, since it's still actively supported. I didn't throw away my hardware, and still might come back someday, but with my limited free time, I chose that route.
