If you’re building a large project with many parts and you want to exchange information between the different microcontrollers you might consider using the CAN bus. It’s a communication bus used in all cars and some industrial machines. Because of that it’s not super well known in the maker community.
The barrier to experiment with CAN is higher than other buses because you need specialized hardware.
I’ve had an idea for a while to build a Poor Man’s CAN bus to let people mess around with CAN with common components. I finally gave it a shot last night and it worked great! I wrote up my findings.
tl;dr you can prototype a CAN bus with 2 Photons and 1 AND gate. Read up for more details and a little CAN primer