The Google Firebase FriendlyChat Objective-C Sample Code by Google demonstrates the procedure for deploying the Objective-C language when using firebase codelab to build cross-platform iOS chat applications.
Cloud-based messaging app Telegram provides free, open and secure communication across any platform with automatic chat synching across devices. Telegram also provides a dedicated Bot API for building custom bots that users can interact with via messages and commands to perform predefined tasks.
Last month mobile-to-mobile communications company Bump decided to share its technology, which allows for data transfer between two iPhone or Android phones. For example, its flagship iPhone app swaps contact info and photos when two phones "bump" (as in "fist bump") near each other. Bump introduced an API, but to little fanfare.