Turning an Arduino of virtually any sort into a simple AVR 6-pin ISP programmer is old hat. But when Atmel came out with a series of really tiny AVR chips, the ATtiny10 and friends with only six ...
The most common way of programming AVR microcontrollers ... and MISOs coming out of it will program every AVR you’ll ever come across. The ISP does have a downside – fuses.
The internal flash and EEPROM memory of many of the AVR microcontrollers can be programmed "in system", without removing the circuit from its socket, through the ISP (In-System Programming) interface.