Teensy 3.6 and 3.5 - USB Microcontroller development system

The Teensy USB Development Board is a complete USB-based microcontoller development system.

Version 3.6 features a 32 bit 180 MHz ARM Cortex-M4 processor with floating point unit. All digital and analog pins are 3.3 volts. Do not apply more than 3.3V to any signal pin.

Sparkfun has a good Setup Tutorial

These datasheets are a useful reference

Teensy 3.6 32 Bit Arduino Compatible Microcontroller

Teensy 3.6 32 Bit Arduino Compatible Microcontroller

Teensy Version 3.5 features a 32 bit 120 MHz ARM Cortex-M4 processor with floating point unit. All digital pins are 5 volt tolerant.

Teensy 3.5 32 bit 120 MHz ARM Cortex-M4 processor with floating point unit.

Teensy 3.5 32 bit 120 MHz ARM Cortex-M4 processor with floating point unit.