The NodeMCU is a wonderful development tool for prototyping, creating, and building IoT (Internet of Things) and any random electronic project that requires a microcontroller and/or WiFi access, it can even be used in place of Arduino in many cases. ESP8266 is a highly integrated chip designed for the needs of a new connected world. It offers a complete and self-contained Wi-Fi networking solution, allowing it to either host the application or to offload all Wi-Fi networking functions from another application processor.
ESP8266, the onboard SoC, has powerful on-board processing and storage capabilities that allow it to be integrated with the sensors and other application specific devices through its GPIOs with minimal development up-front and minimal loading during run time. Its high degree of on-chip integration allows for minimal external circuitry, and the entire solution, including front-end module, is designed to occupy minimal PCB area.