F-droid works perfectly well on any Android device, and is a viable alternative to Google Play (for some users). Android .apk files can be installed on any Android device with one switch flipped - and the first time you attempt to install an .apk file, it points you to the setting. Chrome extensions can similarly be packaged and distributed from another source (i.e. GitHub) and are treated as first-class chrome extensions alongside their store-installed counterparts. Apps installed on an iPhone via Xcode (only available for macOS, which is only available on Apple hardware) expire after 7 days and refuse to open unless they are re-deployed. They last for a year if the user pays Apple $99/year for a developer certificate.
Google's platforms don't have people spending money as much as iPhone users do, but they are not nearly as locked down or restrictive.