In short, it's a sort of Twitter like thing, but no ads, chronological timeline, not controlled by a single organisation, and federated across multiple instances.
Its a recent new server software and client for the StatusNet "fediverse". StatusNet and the protocols it uses are very old, and a small community of users have been there for like a decade.
Its a federated social network. It is like a cross between Twitter and email. Anyone can start a server and set their own community rules and guide lines. If you or someone on your server remotely follows someone they like on another server then your servers will federate and posts from both will be in the public timeline. Eventually you will have a full timeline of many servers. Though your admin can silence or outright block other instances. Most GS veteran admins prefer their users just block people, as full instance banning is an extreme measure and against the spirit of federation. This is also a future-proof approach to social networking because if your server and its admin are malicious you can either start your own or just move and you still can contribute to the same network of people as before.
Recently a guy named Eugen who goes by @gargon@mastodon.social made Mastodon and a patreon account to support its development.
It has a troubled history, as the early adopters of Mastodon were Twitter and Tumblr users from the far-left pro-censorship crowd. They didnt understand how federation worked but they were paying Eugen's bills so he focused on redundant administration tools instead of more critical fixes (its ok now tho). Many popular Mastodon servers for example cybre.space, witches.town(now dead), and others they maintained big instance block lists and they live mostly in a bubble as they did not agree with the hands off, self moderation (blocking individuals) approach of older GNU Social sites. This bubble is really small though and is not sustainable.
Now, even though Eugen and his audience might prefer Mastodon servers not federate with GNU social servers not every masto server uses a huge instance block list. Anyone can host a masto server same as GS.
Stop there; this is where your comment goes off the rails. I'm an admin (disclosure - my blocklist: https://github.com/kstrauser/freeradical/blob/master/content...) and see almost none of the far-left censorship you describe, particularly on content. You want to be pro-Trump? Go for it, as long as you're polite and respectful. Sure, people will argue with you, but that's their right to be expressive, too.
GNU Social is an interesting experiment and was quickly adopted by a lot of people who wanted to have literally zero limits on free speech. I initially switched from running a GS node to running a Mastodon instance because the software was orders of magnitude better, but quickly decided that adding a couple of rules (be polite. Don't harass. Respect others.) made for a much better user experience than the wild west "say anything you want" environment of GS. I guess you could argue that those rules are imposing censorship, but much in the same way that outlawing physical assault is a restriction of our freedom to beat people up.
As an admin, here's my take on the matter: https://blog.freeradical.zone/welcome-to-my-living-room/ . You don't have to agree with everything I say, but you don't get to punch my other guests and then whine when I throw you out. In practice, this is hypothetical because I've never had to ban anyone. Turns out adults are perfectly capable of treating each other decently when they know that's expected of them.
Calm down. You're free to block whatever you want for your instance. That's not my concern. If you want to ban certain politocal alignments or specific opinions then your free to do that as well. I disagree with painting such broad strokes like the early mastodon servers did because it leads to quiet/dead instances. It happened to the one I was on and I switched.
There is a market for closed instances, as some people don't want their opinions challenged or to see things they don't like and it's awesome that there's a way to get that. It just shouldn't be the norm because it discourages federation.
Edit: FWIW judging by your blog post and block list you arent an example of what I was talking about so don't take it that way. There are plenty of reasonable Mastodon servers now that repect dialogue it just had a rough start.
I'm enjoying my time with Mastodon so far, and don't generally engage with politically heated discussions on social media anyway, but this is still my biggest concern as things stand right now. Part of the reason Hacker News is so appealing is the comments, in which you can often read opinions approaching a controversial subject from wildly different angles, sometimes leading to fascinating and civil discussions which leave you feeling better off and more well-rounded for having read them.
Within the currently popular Mastodon servers however, it definitely does feel like a bit of a self-imposed bubble, whereby the about pages espouse civil discussion, but in reality statements or opinions closer to centre on the political spectrum are usually met with hostility and treated as egregiously offensive. I'm hopeful it'll mature over time, settle into a less ambiguous moderation policy that allows for wider coverage of the political spectrum so long as it's civil and ultimately attract a broader range of users.
This is where federation wins really. If your mastodon server wont come out of its bubble nothing is stopping someone from making a new server that does. Instances may die, but the social network as a whole never will.
If I'm wrong about any of this tell me. There's nothing inherently wrong with a blocklist, I just don't like them and I'm just pointing out that it's a thing. I'm just posting my personal observations.
Social media is what is replacing our town square, and the potential for someone to walk by and say "Nah, mate, that's fuckin stupid, and here's why" will be sorely missed in the environment that bubble-ists desire.
