MicroPython is a Python interpreter that runs on many of microcontrollers available today. It can be though of as an operating system that will run Python code. Like the Arduino platform, MicroPython will allow you to control hardware to blink LEDs, read sensors, control motors on any supported board – using Python! There are boards available for just about every task: From the tiny, low cost ESP series of WiFi microcontroller right up to the powerful, fully featured, Teensy.
So, why use it over Arduino? There are technical limitations and differences in both platforms so choosing the best one will be very project specific. We suggest having a quick read of this helpful overview put together by Adafruit!