ESP8266 Arduino Core is the Arduino core for the ESP8266 WiFi chip. It brings support for the ESP8266 chip to the Arduino environment, allowing you to write sketches, use familiar Arduino functions and libraries, and run these directly on ESP8266 without the need for an external microcontroller.
ESP8266 Arduino core comes with libraries that enable it to perform a number of things. It can communicate over WiFi through the use of TCP and UDP; it can set up HTTP, mDNS, SSDP, and DNS servers...