Zanzito is an app that acts as a bridge between your Android phone and an MQTT server. MQTT is a lightweight means of communication between systems, such as your home automation system and the various sensors and hardware devices in your home.
The MQTT protocol is based on the principle of publishing messages and subscribing to topics, or "pub/sub". Multiple clients connect to a broker and subscribe to topics of interest. Clients connect to the broker and publish messages to topics.