The C64NET Wifi Firmware is an api for communication between a serial terminal and the ESP8266. It simulates the old-style Hayes "AT" commands, so that the ESP8266 appears to the terminal as if it were a Hayes modem. These "AT" commands may then be issued to the ESP8266 in order to force it to connect to a wireless access point, and from there to make one or more manageable connections to the internet. It also includes a streaming serial "telnet" mode, and server/port listener capabilities.
This document details the API and AT command set.