The Teensy is a complete USB-based microcontroller development system, in a very small footprint, capable of implementing many types of projects.
All programming is done via the USB port.
Version 3.5 features a 32 bit 120 MHz ARM Cortex-M4 processor with floating point unit.
All digital pins are 5 volt tolerant.
Actual size is 6 x 1.8 cm
All Teensy boards are shipped assembled and fully tested.