- 16K of flash memory, the most of any ATtinys (And matching the ATmega168 used in older Arduinos).
- Up to 18 digital I/O pins (close to the 20 you’d get on an Arduino).
- Two hardware UARTS (optionally usable as SPI ports), vs. 1 each on an ATmega328 / Arduino.
- 12 analog inputs (vs 6 on an ATmega328).
- 4 PWM outputs (vs 6 on an ATmega328).
I’ve modified the arduino-tiny core to add support for the ATtiny1634 (Edit: Moved from Google code to Github in 2015). Additionally, you also need an upgraded avr-gcc toolchain. On the Mac, I recommend AVR-Crosspack, which can also be retrofitted into the Arduino IDE.