The Director provides a quick overview of what Hydrogen is currently doing. It can be opened by pressing Alt + D or by via the View option in the Main Menu.
The Director shows you the song name, a visualization of the Metronome, and the Tags. Just below the metronome you can see the latest tag, and below that the next upcoming tag. This way you have a nice overview of what is going on, and what is about to happen in the song.
This comes in very handy when you are recording a song, or if you are using Hydrogen live on stage.