Certainly nothing that couldn’t be done on another platform, but Apple has done a great job of locking us in. iMessage (including playing the games via iMessage

Certainly nothing that couldn’t be done on another platform, but Apple has done a great job of locking us in. iMessage (including playing the games via iMessage), FaceTime, the built in location sharing features, sharing app purchases, etc. All easily replaced with alternatives, but the friction to get everyone to switch over is tough. My personal systems almost all run Linux, and I do have an android tablet, but for my main communicator, iOS is just so convenient.