Syncthing becomes the solution to these open source systems such as centralized storage like Dropbox...
With Syncthing you have a way to store your data and have it available whenever you want and wherever you wan, using the P2P protocol.
Some of its features are:
synchronize as many folders as you need with different people
responsive web GUI;
cross-platform: Syncthing works on Linux, Mac OS X, Windows, FreeBSD and Solaris. There's also an unofficial Android port;
Syncthing doesn't require advanced configuration and it should work out of the box, both over LAN and over the Internet;
secure & private: the data is only stored on your computers, without using a central server; all communication is secured using TLS;
every node is identified by a strong cryptographic certificate and only nodes you have explicitly allowed can connect to your cluster;
open source app, open protocol.