I'm curious. I've read stuff about it and it sounds good, if a little complicated.
Re: complicated, let me try to explain! Although, I'm still new .
Mastodon is similar to Twitter in that your posts are public and you can reply to posts by other users, as well as re-publish (retweet) them or favourite (like) them. There is also a character limit per post, although it's much higher in Mastodon (500 characters).
It's different from Twitter in that Mastodon is really a network of independent servers (called instances), each run by different volunteers and with different rules. You sign up as a user at one instance publish your posts there. However, the instances talk to each other and exchange posts, so that users on other instances can interact with your posts as well.
If you want to move to another instance, you can relatively easily migrate your profile.
If the admins of an instance decide they won't exchange posts with a certain other instance any more, that is entirely possible and does happen sometimes, I think.
There is also very little of the meanness often seen on Twitter.