I have long been of the opinion that the Server/Client model of social media is a man-in-the-middle attack, enabling the owners of social networks to exploit the basic human desire to connect with friends and family. Sites like Facebook and Twitter would seem to have proven this theory over the last couple of decades, generating enormous profits and manipulating people at a scale and granularity that the mass media of previous generations could never have matched.
The alternative seems obvious; instead of everybody connecting to a billionaire's data center to share photos, video, and status updates, everybody should be able to connect directly to the people they care about.
That's the idea behind Retroshare's friend-to-friend networking protocol, which also includes end-to-end encryption for privacy and friend-of-a-friend routing that enables anyone on the network to reach anyone else so long as they have a six-degrees-of-Kevin-Bacon-style connection to someone on their friend list.
The open-source app, which you can find at https://retroshare.cc (desktop-only), uses that protocol to provide all the features you'd expect from a modern social network; Direct messaging, group chat (with sticker support for the furries =3), Twitter-style status updates, media-sharing channels, discussion forums, file sharing, even plugins for voice and video chat.
I just think it's neat, but unfortunately it has a chicken-and-egg problem common to fledgling social networks. Every few months I make a post about it and occasionally get a few volunteers to trade friend codes and try it out, but since there's no critical mass of people already using it, there isn't much there to entice people to keep using it.