Carbon Copy Cloner++ But it is not automatic, though you can schedule.
I place vitally important documents in DropBox - which allows version management of files in between Carbon Copies, and backs up to the cloud.
Have two disks for CCC - one local, and swap it with one elsewhere weekly.
You might consider having a Time Machine Drive too, though it is not an immediately bootable solution.
Also - a copy is not a backup unless you check it boots and works. It's just a potentially rubbish copy...