Apple added support for third-party apps right in iMessage as part of the iOS 10 release, and thus far the obvious use for this feature has been stickers. Everyone loves slapping stickers in their messaging apps. But, lest we forget, iMessage is primarily an app for communicating with words. And it's entirely possible that some of your friends don't use there words well. If that's the case, consider the Grammar Snob sticker pack: it's a bunch of red-pen corrections for common mistakes that you can slap on you're friends' errant chat bubbles.