Back in time sounds like a good choice for your case.
From the Ubuntu Apps Directory:
Back In Time is a framework for rsync, diff and cron for the purpose
of taking snapshots and backups of specified folders. It minimizes
disk space use by taking a snapshot only if the directory has been
changed, and hard links for unmodified files if it has. The user can
schedule regular backups using cron.
This is the GNOME front-end for the backintime-common package. If you
also install the package nautilus-actions, it can be integrated with
the Nautilus file manager to provide context-menu options.
It creates uncompressed backups in the place that you set in the options, allowing you to set useful elements like:
- Where to save your backups.
- Folders to be included.
- Which folders or files you wish not to be included (by name or
- Choose the period of time after which a backup will be removed and
how many backups you wish to keep.
- and Other useful options.
Once the backups are done, you can gain access to your data via the GUI of Back In Time or by diving inside of your backup folders (see the next screenshot). This way will also allow any other users to access the backup in the NAS from within a different operating system.