Institute a backup routine. I am using Macrium Reflect to perform incremental backups to another machine, a NAS.
Why are you limiting your software search to Free?
Hardware is not free. Why do you think that software should be free?
I haven't used a CD in years. They have gone the way of the floppys before them. I rarely use a DVD as well. I xfer data over the network, or wireless, or use memory sticks/cards.
With multiple drives, you can have multiple, bootable drives of differing OSs. Just select which is the boot drive in your BIOS.