This is a MAX485 shield for Arduino Pro Mini, which can be connected easily by pin headers. With the screw terminal, it is easy to connect to the twisted-pair bus. The item at the end of the bus can be terminated using a jumper.
The idea came when I saw the popular cheap MAX485 boards, which are hard to connect and have much bigger footprint. With this shield you can create a cheap decentralized wired home automation network. Due to its small footprint it is possible to install in small junction box.
Price of the components + PCB is around $2.20