For Android @Zapstore exists and works very well!! 🤙

If you’re on iOS, it won’t matter, you can still only download from the AppStore, unless you live in Europe, they like playing fast and loose. TestFlight is the closest thing to something like that. I don’t think their standards are as high for that so you may be able to slip an app through there. I have seen some pirated movie apps on there on occasion, so it’s not like it can’t be done.