A project example involving Arduino UNO and the ESP8266-01 Wi-FI module for implementing peer-to-peer communication between microcontrollers. The project is centrally based on the Simple-Coap and the ESP8266Firebase libraries.
Notice that the voltage for the ESP8266 is about 3.3V on its working pins (more details are in the report)
Here you can find a short guide on how upload the sketch directly from the Arduino IDE while being connected to the Arduino UNO board.