Jordan Singer makes a bunch of iOS apps, but you'll never find most of them on the App Store. Singer calls them "lil apps," and each one is just that: an ultra-basic tool for to-do lists or sports scores or news reading. All the lil apps are side projects for Singer, who works as a product designer for Square's Cash app, so it didn't bother him too much when most of them were summarily rejected from the App Store. "Apple's response," he said, "for the majority of them, was basically … this does not meet the minimum functionality requirement of the App Store."

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Singer wasn't interested in adding more functionality to his apps. Doing very little was the point of lil apps. So he did what a lot of developers are starting to do: He published the app to TestFlight, Apple's tool for testing apps, and left it at that. Anyone can download and use it, but you have to know where to look.

Apple considers TestFlight a developer tool, a way for app makers to test their own software and get feedback from a few trusted testers before launching into the Wild West of the App Store. Developers are starting to see it as something else: A place to have apps just for them, or just for their friends, away from the prying eyes and poking fingers of a billion iOS users. It's also increasingly a place to build apps and try things outside of Apple's stringent guidelines for the App Store.

Building an app outside the App Store has been possible for years, of course. Developers have long posted code to GitHub, which anyone with a developer account could compile in XCode and install on their phone. Apple's had testing systems for years, too, but they used to require email addresses or device IDs to work. Now, as Apple has simplified the system, anyone with an app can just share a TestFlight link and have thousands of strangers sign up.

The only restriction Apple places on TestFlight apps is that each one can be used by a maximum of 10,000 people at a time, which suits many developers just fine. People are clamoring for access to the cooler apps still in private beta, while indie developers are using TestFlight to find an audience they'd never find in the bowels of the App Store. And there's no cooler way to show your status than to post a screenshot of your own TestFlight, chock-full of the hottest apps nobody even knows about yet.

All this buzz does actually help developers accomplish one of the stated goals of TestFlight: finding people to test their apps. "One of the challenges with testing early products is that some products need users before you can really get a sense for how they might function — go figure," Lowercase Capital's Matt Mazzeo wrote in 2015. Mazzeo was announcing a product called Lowercase Alpha, which invited people to sign up to get texts whenever the Lowercase team came across a cool beta. If you saw something you liked, you'd just respond "GET" and get a link to download the app. You could send feedback with a text, too, and Lowercase would make sure the developers got it. It served a practical purpose, but Mazzeo also understood the in-crowd appeal: "Sign up for Lowercase Alpha and become user zero of the most fun and exciting products before they hit the market," he wrote.

More recently, a few developers have tried to open the TestFlight doors even wider. Thomas Weigt, an iOS developer and consultant at BitSuites, said he went looking for a TestFlight community about a year ago, when he had an app and needed some testers. "I don't really have a huge following or anything like that," he said, so instead he bounced around Reddit and other communities looking for people who might want to give him some early feedback. He noticed lots of people were interested in testing new apps but didn't know where to go.

So Weigt built a website called Departures, which just lists all the open TestFlights he could find. They run from the big companies — right now, users can jump into the TestFlights for Microsoft Word, Spotify and TikTok — to indie productivity apps, developer tools, and an inexplicably large number of VPNs. At first, Weight found them himself, mining Twitter and Google for links to open TestFlights, but more recently developers and users are submitting them directly.

At first, Weigt said, everybody wanted the same thing: Dark Mode. That was the big feature of iOS 13, and lots of users wanted to get their hands on the new low-light hotness before their friends. Now, with iOS 14 around the corner, users seem to really want to test the new home screen widgets.

Apple didn't respond to a request for comment, but its stance on the way apps should work on iOS is fairly clear. TestFlight is not an alternative to the App Store, it's a staging ground on the way there. Developers told me Apple doesn't review TestFlight apps very intensively, other than to make sure they're not fundamentally broken or obviously malicious. And if Apple's already reviewed, say, version 1.0 of your app, they say it won't even look at 1.0.1. It doesn't think of TestFlight as a long-term home for apps.

Yet that's increasingly what TestFlight is becoming. Developers are using it to build things that would never be allowed in the App Store, to get around some of Apple's more-restrictive policies and more-expensive commissions, and to create an app ecosystem that feels smaller and more intimate. The App Store forces every app to try to become a multinational conglomerate, but TestFlight lets them stay mom-and-pop stores.

Used correctly, TestFlight is also an incredible hype machine. Clubhouse, the hottest app in Silicon Valley, is still TestFlight-only even after months of use and buzz. Clubhouse founder Paul Davison said the app hasn't gone public yet while the small team tries to finish it, but keeping the app exclusive also solves a separate problem. "We think it's important to grow communities slowly, rather than 10x-ing the user base overnight," Davison wrote on Clubhouse's blog last month. "This helps ensure that things don't break, keeps the composition of the community diverse, and allows us to tune the product as it grows." If Clubhouse tried to put its app on the App Store without allowing everyone in, Apple would reject it out of hand. (Just ask the folks who built Hey.) TestFlight gives Clubhouse a way to control growth and to keep hold of its own narrative as long as possible.

There are other, more nefarious reasons a developer might want to avoid App Store scrutiny. Facebook's Research app didn't use TestFlight but went through an Enterprise Certificate program that allowed Facebook to break lots of Apple's rules on data collection and device access in the name of understanding how teens use their phones. (Apple ultimately stopped Facebook from doing this.) In general, TestFlight lets developers collect more data on users — because it's ostensibly for figuring out what's not working in their app — and gives them more leeway.

This kind of exclusivity can change the network, too. The people who know what TestFlight is have the app downloaded and are willing to jump through hoops and deal with bugs tend to be a specific kind of early-adopter. That's part of why Clubhouse has the reputation of being a social network just for VCs. For some developers, that self-selecting level of tech knowledge is exactly the point, but it leaves out a big part of the community.

That's part of what Weigt tried to solve with Departures, making these apps more accessible to more people. Singer's working on something similar with an app called Airport, which operates like an app store for TestFlights. "It's been unreal to see the hype" for TestFlights, he said, "especially around those that have this exclusivity and mysterious vibe to them. and I really wanted to try to lean into that." He's still building the app, but it's already available for download, too. On TestFlight. If you have the link.

Eventually, an app like Clubhouse will likely end up on the App Store. (Hard to be worth $100 million with 10,000 users.) But not every app needs — or wants — access to a billion pockets. Some apps are designed for a group of friends, or a single company, or a small neighborhood. Rather than submit to the App Store and hope nobody notices, those apps are increasingly turning to TestFlight. Other apps might require celebrity status or want to skirt Apple's payment systems.

There's also a whole class of developers building apps just for the fun of it, as a form of creative expression. "They don't want to put it on the App Store," Weight said. "They might just want to share with their friends. It's a creative outlet just like painting or anything else." Ryan Hoover, the CEO of Product Hunt, said he's seen an increase in side projects and experiments as well. "People are experimenting and tinkering more, and some people might either be laid off or just thinking about their next thing," he said. As lockdown changes the nature of work and life, too: People are coding their own solutions to life's annoyances.

Most people I talked to are worried Apple might crack down on how TestFlight is used, preventing them from using it as a smaller, more curated and permissive alternative to the App Store. (More than one also pointed out that Apple probably has much bigger App Store things to deal with right now.) But for now, TestFlight is the perfect place for developers to play.

An entire ecosystem of apps lives under the TestFlight surface. Hoover said he's using a cool journaling app and a messaging app he really likes (but didn't want to tell me too much about, such is the hush-hush nature of the TestFlight circles). Mazzeo, the investor who has hoarded and shared TestFlights for years, is currently building an app called Roadtrip that turns commute playlists into collaborative projects. It's already available for download, and users seem to love it. But it's not in the App Store.