My wireless router comes with a USB connector which allows me to plug an external hard drive in and it'll act as a Network Attached Storage. The problem is that I want to backup this hard-drive to the external drive of another computer so that if the NAS drive fails, I don't lose everything.

However, Windows 7 Backup refuses to include the NAS as a location to backup. I can't fool it by mapping it to a drive letter either. Google presents lots of pages on how to backup files to a NAS, but not the other way around.

Can anyone advise me on free software which can do incremental backups of a NAS drive to an external drive attached the computer it is running on? I'm aware of this question but the top answers have one or more of the following issues:

1. They aren't free.
2. The free version cannot backup a NAS.
3. They cannot do incremental backups.
4. They're just a script and therefore have limited other functionality (eg. disk space management, scheduling, compression, etc.etc.)