PJON is a bit banged serial bus protocol for multiple nodes. You may find it useful.
PJON™ (Padded Jittering Operative Network) is an Arduino compatible, multi-master, multi-media communications bus system. It proposes a Standard, it is designed as a framework and implements a totally software emulated network protocol stack that can be easily cross-compiled on many architectures like ATtiny, ATmega, ESP8266, Teensy, Raspberry Pi, Linux and Windows x86 machines. It is a valid tool to quickly and comprehensibly build a network of devices
