Official Quickblox iOS SDK by Quickblox. It provides a link to download the SDK, code samples, and references to add the SDK to XCode and connect to the cloud. To have an idea of the integration possibilities, visual examples present how to create a simple WebRTC, a chat, a localization feature, and a content storage.
Twilio has released a beta version of its Conversations API. The unified API allows developers to aggregate messages across channels (SMS, MMS, Chat, and WhatsApp) into a single conversation. Additionally, administrators can control the conversation and supplement with experiential features.
Messaging just got a lot more interesting to look at. Words say a lot, but a picture is worth a thousand of them; imagine the levels of communication that could be achieved using both. Doodle Republic is a messaging platform that provides the tools to create messages that include words and images. Basically, people chat by creating their own art and sending it to friends as a Chatoon. The Doodle Republic Chatoon API makes this functionality available to developers who may want to include it in other applications.