If you've been watching the news cycle around app bans and the policies around what is and isn't allowed in the app stores run by Apple and Google, you might have also seen references to "sideloading" apps—which essentially means installing apps that aren't available in the Google Play Store or the Apple App Store.
This is actually relatively easy to do, at least on Android. It can give you access to apps you wouldn't otherwise be able to run (usually because they violate one or more app store policies), and it can also enable you to try out early versions of apps before they're released to the masses.
Before you rush to start downloading and installing things, it's important you know that sideloading apps removes the security protections that Google and Apple give you: Their app stores are carefully patrolled for malware, stalkerware, and anything that might try to steal your data or break your device.
By installing unauthorized apps from alternative sources, you're sidestepping these safeguards. Be very, very careful about which apps you choose to sideload—check and double-check the background of these apps and the backgrounds of the developers that make them. In general, you should install apps outside of your phone's app store only if you have a very good reason to. And if you just read that thinking "Oh, I'll be fine, I don't need to do that extra research," you probably won't, and you really really shouldn't install it.
How to Sideload Apps on Android
Sideloading apps on Android isn't particularly difficult, as long as you're cautious about what you install and take into account the security considerations we've mentioned above. That said, it can be a useful way of expanding what your phone is capable of. It also lets you play around with apps outside of the Google Play Store.
To get started, point your mobile browser toward a trusted site that stores APKs (Android Packages). APKMirror is one of the best and most reliable, for example. When you've found the APK that you want to install on your phone, tap the Download APK button and then OK to confirm you understand what Android tells you—that unauthorized apps can harm your device. At the risk of sounding like a broken record, make sure you know what you're doing.
Tap Open, and if this is the first APK you've installed, you'll be asked to go to Settings to confirm that you want to install "unknown apps" from this source. (In this case, the source is your Android web browser.) You'll have to do this only once for your web browser, and you can then tap Install to run the APK and install the app.
If you need to access the install-unknown-apps setting again, you can find it by going to Settings then selecting Apps and notifications, the app in question (usually your web browser), Advanced, and Install unknown apps. You can install apps from file-syncing services such as Dropbox, as long as you enable this feature for the relevant app.
That's really all there is to it—the process might vary slightly if you're using something other than the stock version of Android 10, which is the latest version at the time of writing. In Android 11, the process is changing slightly, so the downloaded app will have to restart once you've given it permission to run.
The biggest challenge with sideloading apps on Android is not how to do it, but making sure everything you install is safe: Android apps are given more rein on your device than they are on iOS, so the potential for an untrustworthy app to do damage or steal data is significantly higher—as long as you stick to known portals like APKMirror and known apps that are well established and widely used, you can minimize your risk.
For the more adventurous, rooting your Android phone is an option: This basically means hacking your Android phone to take off all its limits and restrictions, but it's not for the faint of heart. While it lets you give apps more control over your system—Titanium Backup, an excellent whole-device backup tool, is a good example—it's difficult to do, it's likely to break some of your favorite apps, and it leaves your phone more vulnerable from a security perspective. Unless you have a very good reason, we'd recommend using the APK method rather than rooting to install non–Play Store apps. Besides, the procedure to root you phone varies among devices and even among carriers sometimes, depending on whether your phone is locked. It used to be a popular pastime, but it's much less common now and in many cases more difficult, and that's by design.
Lastly, web apps are sometimes an option if you need to get at apps that aren't in the official Google store. Even if apps are officially available through the normal route, you can always use this trick to access apps—Twitter, Facebook, and so on—that you don't necessarily want on your phone. If you're struggling to find something in the Google Play Store, see if there's an online version you can get at through your Android web browser.
How to Sideload Apps on iOS
Apple's iOS and iPadOS are much more tightly locked down than Android—Apple simply doesn't make it possible to sideload apps on its mobile operating systems in the same way that you can with Android. There's no safety security switch that you can override, but you still have several options for getting unauthorized apps on your iPhone.
The first is to jailbreak your phone: Here you're essentially smashing the lock that Apple puts on iOS and unlocking your phone yourself, using software distributed on the web (the equivalent of rooting on Android). Once you've applied the jailbreak, you can install just about any app you like—apps to change the look of the interface, access the file system more easily, have apps overlaid on top of each other, and much more.
Jailbreaking gives you a lot more freedom in terms of what you can do with your iPhone. The disadvantages are that it's difficult to do, it voids your warranty, it leaves you open to all kinds of new security threats, and it stops you from updating your iPhone as normal. (You'll need to wait for the next iOS version to be hacked before upgrading, which can leave you without security updates, new app features, and in some cases new versions of your favorite apps.) What's more, Apple is constantly and aggressively trying to stop the practice. As with rooting on Android, it used to be more popular, but in recent versions the balance between the effort required and benefit gained has tipped toward effort, so for most people it's just not worth it.
Information is widely available on the web about how to jailbreak your iPhone (although unlike Android, the model of iPhone you have doesn't matter as much), and the free apps you need to do it—typically you'll need to connect your device to macOS or Windows and run the jailbreaking tool from there. Make sure you fully understand the privacy and security implications, and be aware that jailbreaking information can very quickly become out of date. In general, it's not something we recommend.
Another way to install apps that haven't been released in the Apple App Store is to use a program called TestFlight. This is much more reliable than jailbreaking, and it's officially sanctioned by Apple, though it's unlikely that you'll ever come across it unless you're specifically looking for it—TestFlight is a tool for developers to test beta versions of their apps before they're formally launched.
Anyone can download and install TestFlight for free. That's the easy part, but you can't then go and install every prerelease app package you like: You need to be specifically invited to join a beta test, usually via a link sent to you in an email or posted to the web. Open that link in TestFlight and you'll get access to the software code and any beta app updates that arrive thereafter.
Beta releases give you early access to apps and features before everyone else gets them, but expect to encounter some bugs and issues along the way. If you want to get involved, you can find details of open betas at WABetaInfo, as well as on Reddit and various other places online. You can also sign up to access early versions of various Google apps on TestFlight as well.
As on Android, you can also turn to web apps, although Apple polices this quite closely as well. If something has been blocked from the Apple App Store, you might be able to get access to it through Safari or another web browser on your iPhone—the experience usually won't be as good as it is with a native app, but it's better than nothing.