Twitter's been combatting harassment for years. The latest effort: quelling its horde of anonymous, hostile egg accounts. But for many users, Twitter's abuse problem has long since undermined its value as a platform for creative communication. That's what makes Mastodon—a free, open-source, and increasingly popular six-month-old Twitter alternative—so intriguing.

Mastodon has created a diverse yet welcoming online environment by doing exactly what Twitter won’t: letting its community make the rules. The platform consists of various user-created networks, called instances, each of which determines its own laws. One instance could ban sexist jokes and Nazi logos, while another might practice radically free speech. (In this way, Mastodon is not unlike a network of discretely moderated message boards crossed with a Tweetdeck-like interface.) Users choose for themselves which instance they want to join and select from a host of privacy and anti-harassment settings. Oh, and the character limit is 500, not 140. In essence, Mastodon is an experiment in whether individually moderated communities can make a social network like Twitter more civil.

The house rules for icosahedron.website, a popular instance on the Mastodon platform. Each instance gets to set its own rules, and users pick for themselves which environment feels best. The system aims to preserve free speech and keep out trolls. Hover for more detail. icosahedron website

The upshot, at least for now, is that people on Mastodon get to be themselves. “At a certain point in my life, my Twitter account stopped being a diary that other people happened to be able to read, and I had to start having a public presence,” says writer Ingrid Burrington, who joined Mastodon a few weeks ago after catching buzz about it on Twitter. “There’s an expectation of performing a version of yourself.” Mastodon, on the other hand, reads surprisingly free of that kind of brand-conscious, self-promotional posturing. Burrington joined an instance run by “a bunch of nice French feminist anarchists" that has an effusive daily welcoming party for the newest users. In another instance you can find furry cartoons (SFW and NSFW). There's even a word-game community with a rule against using the letter "e."

Mastodon aims for that kind of liberated banter among likeminded users. “I hope people will have more interesting conversations, more nuanced conversations, with less misunderstanding,” says developer Eugen Rochko, who created Mastodon after growing disenchanted with Twitter. Like many others, Rochko sees problems in Twitter’s advertising policies and its ongoing failure to root out harassment. Brands and bullies don’t make for engaged communities. “People lose visibility,” he says. “If you control the platform that you publish on that can’t happen.”

Mastodon's decentralized architecture makes for a more democratic user experience. On Twitter’s turf, you’re subject to the company’s rules. On Mastodon, you choose your own instance, but still send messages to users in other ones. (Rochko compares instances to email. You might prefer Gmail, but you can still send a letter to that uncle who stayed on AOL.) Rochko even shut down the flagship instance—mastodon.social, which he created—to prevent it from monopolizing the platform. Right now, over 140,000 users are spread across nearly 400 instances—up from around 24,000 users a couple weeks ago.

Users wouldn't have flocked to Mastodon were it not for its slick user interface. Mastodon mimics Tweetdeck in appearance, and Twitter—or Instagram, or Facebook—in its easy onboarding process. That makes it an anomaly among Twitter alternatives (like the ill-fated, crowdfunded App.net). “It's the first example that I’ve seen so far of a free and open source decentralized system that's usable,” says Aral Balkan, a software developer and activist for ethical design. Balkan says Mastodon is what Twitter would be like, if Twitter respected users. He credits the suite of privacy and muting tools for creating that kind of environment. “It’s possible to communicate in a controlled way that is more human-friendly.”

Mastodon's fandom doesn’t herald Twitter's demise. “Suggesting that Mastodon will replace Twitter is like asking if Facebook will replace email,” Burrington says. “They do fundamentally different things.” But that utility doesn't guarantee Mastodon's survival, either. Rochko is looking into building what he calls a selection wizard, to help new users find instances that appeal to them. More features like that will improve the Mastodon experience, but will be difficult to scale for free. And as the number of instances grows, moderators will inevitably run into censorship issues—something Reddit, a website founded on the principle that its manifold subreddits should govern themselves, has struggled with as it's grown.

Still, Mastodon shows what another kind of online system could look like. In our recent story on Twitter’s paltry efforts to curb harassment, we wrote: “At the moment, it’s still humans who have to figure out how to stop the tech they’ve created from doing any more harm.” For now, Mastodon is a working example of exactly that.