This is an example output device plug-in for Uranium. Uranium is the underlying framework used in Ultimaker Cura and NinjaKittens.
Output devices are meant to communicate with a place where the output of the application can be stored. For instance, an export of the model or a result of computation.
An output device plug-in starts with a start() method and stops with a stop() method. This allows you to make a connection with your device while in the loading screen. This should then add one or more OutputDevice instances. For instance, a plug-in could continuously listen for incoming internet connections and add an output device whenever a new connection is made.
The actual output device finds the desired file type to write with, and then provides that file type's file writer with a stream that it can write to. The file writer does the rest.
To package your plug-in, compress your plug-in folder in a .zip archive and rename that archive to get the .plugin extension. These .plugin files can be dropped into any Uranium application to be installed.