I'm always curious here what counts as Social Media, and what's just a useful site?
Github? HackerNews? Reddit? Facebook, but only for FB Marketplace which is now a better local sales site than Craigslist?
What makes it social? Originally with FB and before it with MySpace it was the ability to put up a page about yourself, and then chat with others. HN has a profile and communication, so do the others listed.
For the modern definition of social, nowadays: incentives to generate engagement (connect with people, post, like, comment) to build up data to drive advertising sales.