If you’re looking for a Facebook/Instagram/WhatsApp alternative that’s #open-source and has social features, then keep an eye out for the upcoming Signal release. It’s still not the best messenger, that would be Element which is open-source as well, but uses an open-standard for communication, which is matrix.org. This means you don’t have to use the Element app, as long as the open-standard is used, you can communicate with other people. That prevents vendor lock-in, such as with WhatsApp, but unfortunately, also Signal. You can run your own Signal server, because that’s also open-source, but the Signal network doesn’t allow federation. So you will only be able to text to people connected to your server. Matrix does provide federation and you can run your own server and connect it to others.