You mentioned you didn't want to use the cloud, for backup purposes though I'd like to mention Crashplan, which can use the cloud, but not necessarily and still has a lot of handy features.
Here's the website:
https://www.crashplan.com/
Now I'll start off by saying the major drawback of Crashplan is that it uses Java and can use a lot of memory depending on how much data you have to backup, however I find it's a great piece of software for backup and I have it running on my NAS at home. I pay 5.99$ US/month (probably around 7 AUS) to get the cloud component, so I have a encrypted backup archive stored in their data center as well. However you can ditch the cloud completely and use the software's other features which I'll highlight below.
The free version of Crashplan can backup to an external archive, like an external HDD or a NAS, the backups are always encrypted and you can choose the level of encryption.
Something else that's handy is that you can backup your archive to a friend's PC (or another of your PC's) and vice versa for more redundancy, and you can do this for free, the subscription only adds the cloud component for 1 machine. Crashplan also has unlimited versioning and proper incremental backup, so you can restore back in time, in case you get ransomware like cryptowall and all your backup archive ends up encrypted, you can simply restore a backup from a later date before the virus encrypted everything.
These features can be difficult to make good use of though, if you have high amounts of data and are accumulating more at a high rate and you & your friends have slow internet connections, because the ongoing backups would be slow to complete, so you should always have a local backup first & foremost.
I really suggest keeping your data in more than 1 place and services like this can make this an easy process.
Since we're on the topic of backups, something I'm really interested in, I'll just briefly mention how my backup is setup, just to share some ideas.
I have a NAS with 4x 4TB HDDs in a RAID6 configuration which gives around 7.3TB of storage and allows for 2 drive failures before you lose the data, on my NAS I have OneDrive (Microsoft's Cloud) & Crashplan running.
Now for practical use I put all my data on OneDrive where I have 10TB of storage available, I also upload my data there whenever I have a chance while I'm traveling. As you all know, astrophotography can accumulate crazy amounts of data, especially if you do timelapse too!
Crashplan is purely the backup part, I just have it take a backup of my OneDrive folder, as all my stuff is there. So it will first backup to another machine on my LAN network, which it will do fast at ethernet speeds, then it will start uploading to the Crashplan cloud, which takes a while due to slow upload speeds.
My NAS is connected to a UPS as well in case of power failure.
If a drive fails, I replace it and rebuild the array & hopefully another drive doesn't fail while doing so. If my data amounts start reaching 7TB (I don't expect they will for many years), I will expand the array with another 4TB drive and get around 10TB.
But even if the array on the NAS fails, the house burns down or everything gets stolen, I still have everything on the Crashplan cloud. Even though it would take ages to download, that's what I like about having a backup in the cloud.
Now what I would've liked to add to my setup is a backup archive on a friend's NAS that lives close to me, so I had a local backup that isn't in my house, unfortunately none of my friends have 2TB of storage available for my data, or a NAS.
I didn't even make this setup until about a year ago. Before then all my data lived on a single vulnerable 4TB external harddrive & uploaded on, first Google Drive for a while, and then OneDrive. This was not a good 'backup' setup and I'm just lucky my harddrive didn't fail and I didn't get any ransomware. Harddrives all fail at some point.
I worked as an IT-Technician for a long time and had too many instances of people losing all their data because it was only located in a single place. In some cases data recovery was able to recover some of the customer's data, but the data recovery in many cases cost many many times more than what the setup I outlined above would cost you.
