Mongoose OS is now officially recommended by Espressif Systems as a firmware toolkit for ESP8266 and ESP32:

• http://espressif.com/en/support/download/sdk
• http://espressif.com/en/products/software/esp-sdk/overview

Mongoose OS is an open source Operating System for the Internet of Things:

• It reduces time and costs of firmware development by up to 90%,
• Provides reliable, ready to go infrastructure for commercial products,
• Has high security standards, including flash encryption and external crypto chips support.

Using Mongoose OS developers can code firmware either in C or JavaScript and seamlessly connects products to the preferred IoT Cloud.