A binary clock, or more accurately a binary-coded decimal clock, shows each digit in binary. I first saw one at a friend’s place and it served as an interesting ice breaker.
The below image is from Excel. Specifically, it is an Excel chart, though most would be hard pressed to recognize it as such. It represents the time 14:30:26 (i.e., 26 seconds past 2:30 pm).
For a version in a page by itself (i.e., not in a scrollable iframe as below) visit http://www.tushar-mehta.com/publish_train/xl_vba_cases/0907%20Binary%20Clock.shtml