This is a project for using the ESP SDK (for ESP8266) on Haskell via Ivory. It is specifically for the non-OS SDK (that is, not involving the RTOS). (TODO: Should that be Espressif SDK, not ESP SDK?)
See ESP8266 Non-OS SDK API Guide at https://espressif.com/en/support/download/documents for a reference on the API that this is wrapping.