Introduced In: 10.5 "Leopard" (2007)
If you were looking for a software to backup all your important files, there were and are plenty of options available on the market. But Apple was the first to include backup software into its operating system for free. And it was easy as hell to use. With a FireWire external hard drive you could set up Time Machine to make incremental back-ups. God forbid your computer were to crash, you could go back to anytime in your back-up history and restore your machine.