GNU Jami (pronounced Guh-nu Ya-mi) is a peer-to-peer cross-platform messaging and VOIP application. It uses an API called the Jami Distributed Network, meaning that the Jami network has no single point of failure. If you're familiar with TOR you'll understand where this is coming from.
Best part is that Jami is a GNU package; it will always be free/libre software or else Richard M. Stallman perself will break the kneecaps of every developer on the project /half-joke.