Esp8266 + Atmega328 dev board. Discontinued project, with Esp32 its no longer needed.
Esp8266 and Atmega328 share the i2c bus, Esp is the master and the mega acts as a i/o expander, with adc,pwm,serial and other libraries support. With custom i2c library the Esp can initialize any library on the mega and it will run in the background untill the esp request data or sends data.
