Node MCU

A cheap open source IoT platform is NodeMCU. It originally included hardware based on the ESP-12 module and firmware that runs on Espressif Systems' ESP8266 Wi-Fi SoC. Support for the 32-bit ESP32 MCU was later added.
Models Of Node MCU: 
8. ESP-14
History Of Node MCU: 
The ESP8266 was released shortly after NodeMCU was developed. The ESP8266 started being produced by Espressif Systems on December 30th, 2013. On October 13, 2014, Hong uploaded the first file of the nodemcu-firmware to GitHub, launching NodeMCU.  After two months, when developer Huang R contributed the gerber file for the devkit v0.9 ESP8266 board, the project was expanded to incorporate an open-hardware platform.
Later that month, Tuan PM contributed to the NodeMCU project and converted the Contiki MQTT client library to the ESP8266 SoC platform[15]. As a result, NodeMCU was able to implement the MQTT IoT protocol by utilising Lua to connect to the MQTT broker. Another significant update was released on January 30, 2015, when Devsaurus added support for the NodeMCU project's u8glib[16], which made it simple for NodeMCU to operate LCD, Screen, OLED, and even VGA displays.
The GPIO (General Purpose Input/Output) on NodeMCU is accessible, and the API documentation includes a pin mapping table. 
I/O index ESP8266 pin
0 [*] GPIO16
5 GPIO14
6 GPIO12
7 GPIO13
8 GPIO15
10 GPIO1
11 GPIO9
12 GPIO10