This is the the date and time written out on the face of a clock where numbers go where the ends of hands would be.
The second goes around once a minute, the minute once an hour, the hour once a day (24 hour time), the day once a month, and the month once a year.
Each digit of the year goes around separately. The year goes around once a decade, the decade once a century, and so on.
Each number moves continuously and changes to the next number right as it passes the moment of change. Thus the hour reads '23' while it approaches the top of the clock and flips to '0' at midnight.
The yellow and dark grey circles on the hour ring mark the sunrise and sunset (if your location is set correctly). The time is always displayed in the local time according to your computer. Setting a location far away still shows the sunrise and sunset for that location in your local time zone. (My computer in Boston may tell me that sunrise in San Francisco is at 9am.)
Marks in the day ring show the previous and next moon phase (new, quarter or full).
I was inspired to create this clock by the Long Now 10,000 Year Clock.