There is an App that I use often. It's called "WiFiFoFum": it's a WiFi scanner - it checks all the WiFi channels to see which are in use. It's essential when troubleshooting misbehaving WiFi installations, to find a clear piece of spectrum.
It was available from the App Store until a couple of years (or so) ago. Then it was pulled, and soon after that the (paid for) copy on my iPhone was deleted (by Apple, I assume, because I certainly didn't). I contacted the developer, and got a standard reply that Apple had pulled it because it "contravened their policy". It was then offered on Cydia, so I jailbroke my iPhone and reinstalled it. It still works well. It means I can't update to the latest iOS until that's been jailbroken, but with all the problems recently that is probably a good thing.
Recently, another App was launched on the Apple Store, also called WiFiFoFum, which does something completely different. Sneaky, I thought.
If it's not a closed garden, it's one with a strict head gardener who won't allow just anything on his patch.