The Nano Every is Arduino’s 5V compatible board in the smallest available form factor: 45x18mm. The Arduino Nano is the preferred board for many projects requiring a small and easy to use microcontroller board.
The Arduino Nano Every is an evolution of the traditional Arduino Nano board but features a lot more powerful processor, the ATMega4809. This will allow you to make larger programs than with the Arduino Uno (it has 50% more program memory), and with a lot more variables (the RAM is 200% bigger). An Improved Arduino Nano If you used Arduino Nano in your projects in the past, the Nano Every is a pin-equivalent substitute. The main differences are: a better processor, and a micro-USB connector.
More information is available on the website of Arduino.