Yeah, so I'm on Mastodon.
If you want to join this 'instance' of Mastodon and follow me, use this link.
Both are invitations to mastodon.social — which is the most popular but also only one of many ways to use Mastodon — but you don't have to do either to use Mastodon. You could, instead, go to Join Mastodon and get an overview and then choose from any of a vast number of instances of Mastodon. Think of it — in a limited way — like email: I could have Gmail, you could have Yahoo Mail (but why would you?), but we can still write to each other. You can even set up your own instance of Mastodon if you have a server and are feeling hospitable. And then later, if you want to, look me up.
Here are links to intros to Mastodon at PC Mag and LifeHacker (the later's a bit dated, referring to a tool that lets you look up your Twitter followers, but Twitter's changed it's API, so the tool no longer exists.)