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I use IDrive for this. It runs right on my Synology NAS, doing scheduled backups of the data it contains. The pricing is pretty reasonable, too.

Heads-up for anyone considering IDrive — there's a "90% off" welcome promotion for the first year that's not really obvious on their website: https://www.idrive.com/idrive/signup/el/welcome90

(Disclosure: I work for Arq Backup)

Arq will back up files that are on your NAS, or anything else you want it to back up.

SyncThing, perhaps?

Amen. Everyone: If you were using CrashPlan for simple p2p backups like this, use SyncThing now. It has versioning, it's open source, and it's secure. Made my day... I will enjoy donating to their project.