Earlier quoted context omitted.
More seriously: Syncthing exists, and it is beautiful. I set my grandmother up with Synctrayzor and she doesn't know the difference between that and Dropbox. It is missing the ability to share things with a direct link, or share a repository or folder "easily" (read: in the same way it's done with Dropbox), but the trade off has been worth it for me.
Which cloud backend do you have it sync to?
You run it on your machines and they will sync among themselves. No need for any cloud backend.
Some people with Synology or QNAP run an instance on their NAS.