What?: Social.coop is is an experiment in user-controlled social media. It is a community hub for people interested in co-ops and development of free/libre social media - these define the common core field of discussion, though they are far from the only things discussed.
We primarily run a MastodonMastodon Mastodon is an open source federated micro-blogging platform.
The Mastodon documentation site https://docs.joinmastodon.org/ covers what a microblog and federation are:
Similar to how blogging is the act of publishing updates to a website, microblogging is the act of publishing small updates to a stream of updates on your profile. You can publish text posts and optionally attach media such as pictures, audio, video, or polls. Mastodon lets you follow friends and discover new ones.
Federation... social media server: one node in the Fediverse, a federated network of social media applications which communicate using the Activity Pub and OStatus protocols.
Why..., which is considering joining so SC members get access to meeting capabilities.