NodeMCU is a low-cost open source IoT platform. It initially included firmware which runs on the ESP8266 Wi-Fi SoC from Espressif Systems, and hardware which was based on the ESP-12 module. Later, support for the ESP32 32-bit MCU was added.
We use NodeMCU to control our home automation systems. It is a great way to get started with home automation, and it is a great way to learn about IoT.