Package bibliotek is a library for the Hemtjänst ecosystem.
It comes with a few different packages, most importantly client, server and transport.
The client package lets you create new devices and register them onto MQTT, so that other things can become aware of it. For example, if you wanted to take devices from an IoT gateway like the IKEA Tradfri gateway and make them available as Hemtjänst devices, this is where you'd start.
The server package lets you observe all existing devices, subscribe to state changes as well as change the state of existing devices. This is useful if you want to create a bridge to somewhere else. A HomeKit bridge could be implemented with it, or exposing device information through another medium, like providing an HTTP API.
The transport package contains some MQTT related utilities. You'll likely never need them, aside from transport/mqtt.Flags() so you don't have to define all the different flags for setting up a connection to an MQTT broker for ya CLI utility yourself.