Just discovered pydio (https://pydio.com).

I didn’t now this nice little file sharing tool before. A partner of my agency uses this OpenSource application to share files with customers and partners.
It looks very nice, is responsive, provides native apps for iOS and Android, file synchronization over all platforms, flexible access control list (ACL) and is highly customizable.

And it’s OpenSource!

So I will give it a chance and try it out.