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
NodeMCU is an open source IOT platform. It uses the Lua scripting language. It is based on the eLua project, and built on the ESP8266 SDK 0.9.5.
It uses many open source projects, such as lua-cjson,and spiffs. It includes firmware which runs on the ESP8266 Wi-Fi SoC, and hardwarewhich is based on the ESP-12 module.
It uses CP2102 as UART bridge, and can flash firmware automatically by using nodemcu-flasher. It support apple's MAC OS.
It is an integrated unit with all available resources on board. It is super simple to complement your existing Arduino projects or any development board that has I/O pins available.