Backblaze works with Mac OS and Windows. But the guys that started it are ex-engineers at Apple. A linux client is in the works.
Crashplan can do two things. One is that it works just like all the other providers where it backs up to their servers for a monthly fee.
The other thing it does and it does and it does this for free is it makes it so you can back-up one computer to another computer. Or you could back-up 20 computers to one computer if you wanted. This never hits their server.
So say you have a work computer in the office and a PC at home you can have it shoot off any new or modified files on the work PC and it will get backed up on your home PC. You just need to make sure you have the space to store the files on your home PC.
It seems like a odd thing to build into a product where they want you to buy storage space from them. But they did it and it works well.
But, like I said, I use it so my moms computer is constantly backed-up to my computer. I have a lot of storage space and run daily snapshots of her back-ups so if needed I could easily roll her computer back to where it was at midnight for any of the last 30 days.