There are a couple of options for using MQTT on iOS. Facebook are doing so (they credit libmosquitto in their native Facebook iOS app, and in the Facebook Messenger app).

• It is possible to use libmosquitto on iOS. Marquette is an example iOS app (with source) to control a Nanode.

(削除) There is also an Objective-C implementation of a client from the m2m.io team. This ships with an Xcode project which contains a simple iOS publish/subscribe client, HelloMQTT. (削除ここまで)

• Yet another IOS simple example. https://github.com/tipih/Simple_MQTT This is working on IOS7 with ARC. It also works with TLS.

• mqtt-prowl - Subscribe to topics on an MQTT broker and notify via Prowl

• MQTT-Client-Framework a native Objective-C (works with Swift too), fully featured MQTT client for iOS, macOS and tvOS. There is a demo application MQTTChat and an Introduction

• MQTTInspector an iOS (iPhone, iPod, iPad) MQTT monitoring and testing tool