• a USB device port with cable shield filtering and transient suppression
  • 3.3V LDO with bypass caps and filters to separate analog VDD from digital VDD
  • Schottky diodes to protect the possible power inputs
  • 12.288 MHz crystal for the master clock (pretty useful in audio applications)
  • reset pushbutton with debounce cap and pullup resistor
  • blue LED on pin 32 for the classic Blinky test
  • two breakout headers (all pins broken out except 2 pins for crystal and 2 for USB)
  • the ATSAMD21G18 in TQFP package (max specs for the D21, easier to solder than a QFN)
  • Plus: Full compatibility with Arduino Zero firmware (without debugging options because there's no programmer/debugger chip on the board)