Seafile is a secure, reliable, and performant file sync and share solution. I have been using it since about 2014, occasionally trying out other solutions, but keep returning to Seafile. It has a fairly large feature list and works on every major OS/mobile-device. Self-hosting it has been painless and performance is rock solid. This post describes one particular feature that is useful to me and is present ONLY in Seafile (to the best of my knowledge).
(I am not associated with Seafile in any way. Just a happy user.)