I've tried the extension, managed to add a couple of stations, started playing one, clicked stop and while the sound stopped, so did the extension. The main screen is non responsive as far as I can tell. I've ventured into the github and by the list of bugs I venture that it's not exactly ready for public consumption. As a rule of thumb, I would refrain from recommending Gnome extensions in the future as the whole mechanism seems to be in a constant state of instability.
Dungeon World, and many other variants are based on Apocalypse World (http://apocalypse-world.com/), which should really be given a nod here.