When the neutrino was first detected, renowned physicist I.I.Rabi had the perfect reaction: "who ordered that?" It was a confusing new thing and it wasn't immediately apparent to anyone what to do with it.
Well that's sort of the way I reacted to Twitter, I'm still a rather reluctant late adopter, and (like most people) I follow way more than I react or post.
Now we have Mastodon! Yay. And my first reaction is: "who ordered that?"
It's an open-source distributed messaging system which has a lot of similarity to Twitter. Anyone can post anything, link to anything, and comment on anything. There are likes (favorites) and "retweets". Pictures and videos. And there is a content moderation protocol which is designed to keep a certain level of sanity - eliminate child pornography, for example.
People who were unhappy with Elon Musk's acquisition of Twitter have searched for alternatives, and to date Mastodon has emerged as the most popular alternative. It's vastly smaller than Twitter, and there's such a huge network effect already in place that it's impossible to imagine Twitter being supplanted. But unlike some moves in the physical world - like moving to Canada - online you can be in two places at once.
The biggest difference is that with Twitter, the whole thing is operated by one company, whereas with Mastodon there is a network of servers cooperatively communicating, but each operated by separate companies or organizations. Kind of like with email, you have to choose who you want to be "your host", and then after that you can interoperate. Your host is responsible for managing your account; it could go off the air, taking you with it. And it decides what to moderate - different hosts have different policies.
I decided to see what the fuss is all about, and opened an account: @firstname.lastname@example.org. Now I can post there, and read Mastodon messages, and follow people there. Yay. But if I want to check on flooding in Santa Barbara, Twitter is going to have way better information. Way more junk and ads too, but so it goes.
[Update, yay, dlvr.it supports Mastodon. So now when I post here, a link is relayed and posted there, just like with Twitter.]