I had a constraint of having to use existing unshielded and untwisted wires in parallel to 220V mains wiring. Basically I'm doing DIY thermostats for floor heating and only 4 copper conductors were available. Stumbled on PJON with Softwarebitbang and it seemed to fit the bill, although they do recommend twisted and/or shielded cabling.

With no background in hardware and Arduino there was a lot of learning to do, but in the end I'm really happy that it's been working flawlessly for a few months now and one copper conductor is even unused.

Don't have an oscilloscope so no idea how "ideal" the situation is on the wire with regards to electrical interference, but for anyone interested, it's running in a star topology with wire lengths about 20 metres on, with ESP32's as the microcontrollers.

edit: thanks for PJON, gioscarab!