Have a hefty script that simply won’t fit on your Arduino? With the Arduino ISP you can get rid the bootloader on any Arduino AVR-based boards and use the space the bootloader normally takes up. Simply upload a sketch with the external programmer and the boot loader is removed, leaving behind extra space for your sketch. You can also use the Arduino ISP to burn the bootloader back on to your Arduino, if you accidentally corrupt the bootloader.
The Arduino ISP requires 5V to run and uses the ATtiny44 micro controller. It connects to the target board via ICSP and connects to a computer using a micro USB cable. You can buy it online from the online Arduino Store for €12.00.