Three faces move against a fixed hand: solar year, moon, and week.
Disk Clock takes the idea of clock and turns it inside-out by moving the faces instead of the hand. Disk Calendar extends the time period to week, moon, and year.
This is a calendar of sorts, built on natural cycles. Since the regular pace of a 'clock' doesn't align well with irregular months and leap years, the pace is even. Thus, the year follows the solar year, and a moon stands in for a month. Weeks are thankfully regular, and work just as you'd expect.