ESP32

The successor to the popular ESP8266 is the ESP32. Although slightly more expensive, the ESP32 offers a dual-core processor over the single-core of the ESP8266, support for Bluetooth, and more GPIO pins. The LOLIN32 ESP32 (the following photograph) features a built-in temperature sensor and a hall effect sensor. A hall effect sensor measures magnetic fields. This sensor is used for such things as indicating when doors are closed and measuring the revolutions of a wheel (such as what's in use for a bicycle speedometer):

The following MicroPython code will read and then print data from the hall effect sensor of the LOLIN32:

import esp32
import time

while True:
    print(esp32.hall_sensor())
    time.sleep(1)

The ESP32 is a low cost, yet powerful, microcontroller. This makes it one of the best platforms for MicroPython development.