I have built a clock which shows the phases of the moon; it also displays the dates of forthcoming lunar quarters along with sun and moon rise and set times. There is a picture of the clock on http://www.hinch.me.uk/lunartick.jpg
and one of its internal construction on http://www.hinch.me.uk/internals.jpg
The pointer indicates the current phase of the moon. By default the Text LCD shows the time and date along with the exact time and date of the next lunar quarter. By pressing the leftmost button subsequent quarters can be displayed. The second button causes the display to show sun and moon rise and set times for the current day, whereupon pressing the first button will predict rise and set times for subsequent days. The leftmost LED lights at times when the moon is up, and the rightmost LED indicates wireless network connectivity.
The clock runs a C program on the SBC, and it runs entirely independently of the network. However the network allows the SBC to re-initialise its clock after a power outage. It also keeps the time accurate to within a second or two by virtue of the SBC's periodic checks on internet timeservers. However even with the network down the SBC keeps remarkably good time: mine gains a few seconds per day.
Woodwork, metalwork and software by me, hippy artwork courtesy of my wife Sue, who christened the device "The Lunartick".