Let me tell you about the greatest little software you've never heard of. It's called Agora Project, and it's the creation of a young programmer from France.
Agora Project bills itself as team collaboration software, but mostly it has all the same features as a typical social network: news, forum, event calendar, image galleries... you name it. Also built-in instant messaging, and even video chat if you have access to a Jitsi server. Only user profiles are de-emphasized.
Agora Project is also very lightweight at just 17MB for a fresh install, including documentation and sample data. And being in Softaculous, you can easily install it on any old web host. Sounds scary? No worries, hosted plans are available at good prices. Thanks to the General Public License and built-in data export, there's no risk of lock-in.
One other thing I like here is simplicity. There are enough features to help you with work, but not huge confusing tables of obscure checkboxes like in some of the competition. You can change colors, backgrounds, and the logo. Also which of nine modules to enable in each workspace. By the way, you can create any number of workspaces, and make some of them public so that guests see them without an account. Even public spaces have fine-grained access control lists for privacy.
That's a nitpick anyway. Agora Project is very fun and useful, and I hope to get a lot done with it. Highly recommended.