When Twitter quietly updated its developer policies to ban third-party clients from its platform, it abruptly closed an important chapter of Twitter’s history. Unlike most of its counterparts, which tightly control what developers are able to access, Twitter has a long history with independent app makers.

Now, the developers of some Twitter clients are turning their attention to another upstart platform: Mastodon. This week, Tapbots, the studio behind Tweebot, released Ivory, a Mastodon client based on its longtime Twitter app. Matteo Villa, the developer behind Twitter app Fenix, is testing a Mastodon client of his own called Wooly. Junyu Kuang, the indie developer behind Twitter client Spring is working on a Mastodon app called Mona. Shihab Mehboob, developer of Twitter app Aviary, is close to launching a Mastodon client called Mammoth.

The one-time Twitter developers join a growing group of independent app makers who have embraced Mastodon, the open-source social network that’s seen explosive growth since Elon Musk took over Twitter. The decentralized service now has more than 1.5 million users across nearly 10,000 servers. That, coupled with Mastodon’s open-source, “API-first” approach, has attracted dozens of developers eager to put their own spin on the service.

Paul Haddad, one of the developers behind Tweetbot and Ivory, says Tapbots started working on a Mastodon client late last year as they started to grow nervous about the future of Twitter’s developer platform.

“They [Twitter] had absolutely been making huge strides and opening up their API platform, but clients like ours were always going to be second- or third-class citizens,” says Haddad. “Whereas with Mastodon, that’s absolutely not the case.”

Thomas Ricouard, the developer behind Ice Cubes, a Mastodon app that launched earlier this month, says that he had considered building an app with Twitter’s API in the past, but decided against it because it was “looking more and more limited as the days passed.” At the same time, he says he noticed fewer and fewer familiar faces on his Twitter timeline. “Loving open source software,” he says, “I quickly saw the opportunity [for Mastodon].”

Ice Cubes launched in the App Store January 19th, and it has already won the praise of reviewers and has dozens of contributors on GitHub. Even Twitter co-founder Ev Williams, who has been more active on Mastodon lately, uses the app.

On its part, Mastodon has welcomed developer interest even though it maintains its own mobile apps. “It’s exciting because it means that a lot of very talented people are investing their time and resources into building on the platform and ecosystem that we have built up,” Mastodon founder and CEO Eugen Rochko tells Engadget. “Third party applications are incredibly valuable for a platform because that’s where the power users go … it benefits everybody because the power users are the people who create the content that everybody reads.”

Developers’ contributions also have the potential to influence the direction of the platform itself. Just as Twitter’s earliest developers had an outsize impact on the service, some developers now see an opportunity to similarly influence Mastodon.

Both Ricouard and Haddad noted that official Mastodon apps currently don’t support quoting — the Mastodon equivalent of a quote tweet — but some clients, like Ice Cubes and Mona, do. “I think the client developers are able to implement that feature within the app, we’re probably going to push it to go higher up on the radar of the Mastodon server developers,” Haddad predicts. Mastodon so far hasn’t publicly committed to adding quotes but Rochko, who was once adamantly against the feature, recently said he’s considering it.

Mastodon developers have experimented with other unique additions, too. Ice Cubes has Chat GPT-powered prompts that will spice up the text of your post (or “toot” as they are known to longtime Mastodon users). Wooly groups notifications in batches, similar to Twitter. Tapbots is working on a Mac app that will sync with Ivory’s iOS app, much like Tweetbot did across platforms.

“Mastodon is in the [same] early phase Twitter was, where third party apps will have a big impact on the future product focus and development,” says Ricouard.

Rochko says that while he’s happy to see the growing number of Mastodon clients, he’s not in a hurry to try to replicate their features. Mastodon is still a nonprofit with a small team and a lengthy product roadmap. “It’s definitely interesting to see different ideas tested out and experimented with and I think that long term, there’s probably going to be influence over the official apps,” he says.

Still, not every former Twitter client developer is eager to start over on Mastodon. “I’m not sure if I want to create a Mastodon app but you should definitely check out those other developers who have,” Tweetings said in a farewell post on Twitter. Twitterrific’s developers are also unsure if Mastodon fits into their future plans.

Much will likely depend on if Mastodon is able to maintain its current growth and continue to attract new users. And as much as many former Twitter users see it as a replacement, Mastodon is structured very differently, and not everyone finds it as user-friendly as Twitter. Rochko, who started Mastodon in 2017, says he’s optimistic because the site continues to add influential users.

“What’s exciting to me about the latest wave of users on Mastodon is not the numbers but the who. The people who have joined from various journalist organizations, media organizations, politicians, actors, writers, and just you know, famous internet people — like the olden days.”