These days, connecting your microcontroller ... avrdude -p m328p -c arduino -b 115200 -P net:192.168.1.123:23 -U:yourHexFile.hex. The ESP8266 passes the data straight through its TX and RX lines ...

A lot of people have used ESP8266 to add inexpensive WiFi connectivity to their projects, but [Oscar] decided to take it one step further and program an Arduino over WiFi with the ESP8266.