At the developer conference WWDC in 2016, Apple had announced the release of an entire App Store comprised of applications solely meant to be shared with another recipient via iMessage. This announcement opened the doors for stickers, games, and posts to be shared between individuals/groups. My friend Amar and I decided to try out building the collaborative zero-zum ConnectFour game solely through the new iMessage API. Before the iOS had publicly launched and the iMessage App Store was eventually unveiled, Amar and I had finished our working copy of the ConnectFour game playable between two iMessage accounts.
Disclaimer: Potential breaking points are iPads and group chats!