CPP: ESP8266 Arduino core - lvidarte/esp8266 GitHub Wiki
The ESP8266 Arduino core project brings support for ESP8266 chip to the Arduino environment. It lets you write sketches using familiar Arduino functions and libraries, and run them directly on ESP8266, no external microcontroller required.
ESP8266 Arduino core comes with libraries to communicate over WiFi using TCP and UDP, set up HTTP, mDNS, SSDP, and DNS servers, do OTA updates, use a file system in flash memory, work with SD cards, servos, SPI and I2C peripherals.
Here you can view the documentation for the latest development version (out of this wiki):