I had great plans for doing interesting things over the Christmas break, but I ended up spending the time sorting out the household's backups.
Until now, my backup system boiled down to semi-regularly rsyncing to one of two external hard drives, and some of my most important directories being far less regularly dumped into encrypted tarballs and synced to a free cloud storage provider.
My main worries are not having data only at home (one fire, flood or burglary away from losing everything), and not tracking changes to important files - even more of a worry these days with the rise of ransomware. After a few false starts, this is what I've settled on:
I discovered BorgBackup. It does exactly what I wanted: de-duplicating backups, so your backup 'archives' don't waste space (and in fact, you save space if lots of your files are similar), and it isn't hampered by renaming files and the like. That, and the backup data files are encrypted, so I'm not worried about them being backed up to the cloud.
Note to self: send printed copies of encryption keys to friends and family on other continents.
I've used borg with WSL, and uploading files seems to work well enough. I haven't tried cygwin. I couldn't back up directly to an external hard drive (iirc, due to a not-yet-implemented system call in WSL which caused borg to choke), but worked around that by setting up some VirtualBox vms and getting the data to them via ssh.
for pushing data to cloud storage, I'm using rclone. Like borg, a great piece of free software.
I settled on plcloud for online storage. They had a Christmas special which made it pretty cheap to get 2TB for a year. I'm nowhere near that now but if I start ripping our CD collection to flacs, which I want to do in 2018, then I'll be glad to have the headroom.
I also looked at Backblaze B2; they're well regarded and I may yet use them for additional redundancy. Their monthly storage costs are only slightly more expensive than Wasabi, but downloads are cheaper, and if you're going to trust your whole life to some encrypted files in a cloud provider's data centre, I think it's a good idea to to download everything occasionally to make sure that restoring your data actually works.
Needless to say, Amazon Glacier and Google's equivalent (whatever it was called) have ridiculously complicated and scary pricing models for their cold storage options, so they were non-starters.