The Teensy 3.5 is large, for a Teensy. But that just gives it more room for pins, both analog and digital, continuing the Teensy tradition of packing in an impressive amount of I/O and speed. It also has a microSD socket, USB, and can emulate USB devices. Once the Teensyduino software has been added to your Arduino IDE, interfacing with the 3.5 works very smoothly. You can also program it in your favorite C editor and use the Teensy Loader to upload the file to the board. If you need even more oomph, the Teensy 3.6 is available too.
PJRC Teensy 3.5
|Teensy 3.5||By: PJRC|
|Main Processor:||32-bit ARM Cortex-M4|
|I/O Pins (Digital):||37–62|
|I/O Pins (Analog):||25|
|Memory:||1MB flash, 256K RAM, 4KB EEPROM, microSD|