Also known as: Teensy
Teensy is a line of compact, high-performance microcontroller boards made by PJRC, built on ARM Cortex-M cores.1
Overview
The flagship Teensy 4.0 and 4.1 run a 600 MHz Cortex-M7 — far faster than a typical hobby MCU — in a board barely larger than a postage stamp. Teensy boards are Arduino-compatible through the Teensyduino add-on, so they use familiar libraries and the Arduino IDE, but they also expose deep hardware features: many GPIO pins, several UART/SPI/I²C buses, PWM, and strong USB support.
Where it fits
Teensy is the go-to when an Arduino-style workflow needs serious horsepower or precise timing. Its well-known audio library makes it a favorite for synthesizers and effects, and its fast cores suit MIDI controllers, data loggers, and other real-time work. Where a project wants the same class of compute with vendor tooling instead of the Arduino layer, an STM32 is the usual alternative.