DuPAL
Pre-compiled: https://proghq.org/media/dupal/
Quick flashing
make atmega328 AVR_FREQ=20000000L LED_START_FLASHES=8 BAUD_RATE=57600
avrdude -c dragon_isp -P usb \
-p atmega328p -e -u -U efuse:w:0xFD:m -U hfuse:w:0xDE:m \ -U lfuse:w:0xFF:m -U flash:w:optiboot_atmega328.hex