https://github.com/gioblu/PJON/tree/master/src/strategies/So...
All devices listed in the compatibility section are able to communicate over a twisted pair with no additional hardware, as Fred well noted, you just need one wire and connect directly the IO pins. And up to 255 devices can share the same twisted pair.
As you can read in Video Camera Control Jack just used two arduinos, 2km of wiring within his university's network and a couple of pull-down resistors. The protocol works even when the human body is used as a conductor as shows the gif present in the article.
On social compare someone made this: https://socialcompare.com/en/comparison/comparison-of-networ...
I think the comparison between PJON and LIN there is revealing. As you can see LIN handles up to 16 devices, it is master-slave and has a range of 40, with a complex front-end at a relatively high voltage.
PJON is free for use, it is all open-source. We do sell products to fund the development of the project.