The Editor and the Cue windows have an optional area called Editor list. It contains multiple lists: tracks and busses, sources, regions, reusable clips, various markers etc.

The Editor list is not shown by default when you run Ardour for the first time. It can be hidden or shown using View > Show Editor List menu command. The left-hand border of the list can be dragged to show more columns where appropriate (alternatively, you can scroll the bottom scrollbar to see more).

The Cue window displays only a part of all possible lists — ones that make sense for this non-linear sequencer: Clips, Tracks, Sources, and Regions.