Friendica is a distributed social network application that enable users to connect with others via their own Friendica server. It also allows the integration of contacts from other platforms including Twitter, diaspora*, and pump.io.
Friendica is what a true social network should be; it is distributed, open source, secure, private, modular, extensible, federated and, of course, free. Through Friendica, you can post to traditional social networks and also read from them as well. This two-way connection means that, using Friendica, you can engage in conversations with people on Twitter, tumblr and Diaspora*, all through a single unified interface on a single site that you control.
Therefore, switching to Friendica doesn’t mean switching away from your existing social network. It’s not a sacrifice, but an upgrade.
Proprietary applications it could replace: