The Arduino Nano 33 BLE is a Nano-sized board with Bluetooth connectivity and a 9-axis inertial measurement unit (IMU) that adds a compass to the usual gyroscope and accelerometer. This board should not be confused with the Arduino Nano 33 BLE Sense. The two boards are identical except the Arduino Nano 33 BLE does not have any of the additional sensors found on the Sense version of the board (those being a compass/gyroscope/accelerometer, a microphone, a light and color sensor, as well as temperature, humidity, and air pressure sensors).
The Arduino Nano 33 BLE is run by the Bluetooth module from uBlox. This module features an ARM Cortex M4F based microcontroller from Nordic Semiconductor running at 64 MHz. The “M4F” means this micro has a floating point unit in addition to digital signal processing instructions. The microcontroller runs Mbed OS, an operating system for ARM based embedded systems, and your Arduino sketches run on top of that. The Scheduler library supports cooperative time-sharing among multiple threads on Mbed OS and examples are included for the Arduino Nano 33 BLE.
Connectivity on the Arduino Nano 33 BLE is versatile, with the microcontroller capable of being a USB device or a USB host. It can also be a Bluetooth device or a Bluetooth host. This should make the board good for wearables or for building human interface devices.
The form factor of the Arduino Nano 33 BLE matches that of other Nano-sized boards. Its narrow shape and holes for header pins make it breadboard-friendly. It also has castellations along the edge and a smooth bottom for surface-mounting to a PCB. Like the other Arduino Nano 33 boards, this board runs at 3.3V and is not 5V tolerant. Except for the voltage, it is pin-compatible with the Arduino Nano Every. Like other recent Nano-sized boards, the pins are only labeled on the bottom, so you’ll have to keep a pinout diagram handy for prototyping.
The Arduino website offers a good getting started guide for this board. You will need to install support for Arduino Mbed OS Nano Boards from the Board Manager, and the ArduinoLSM9DS1 library from the Library Manager to access the IMU.