bClk

Night clock. Choice of 12 or 24 hr format. Whole rainbow of color choices and variable brightnesses. Guide button leads you to separate page (and disappears after 3 seconds if not tapped). Set color/brightness by tapping on digits so you are less likely to change something while just handling the clock in the dark. Be sure to plug in because it does draw power.
Single tap: change brightness.
Double tap: change digit color.
Display another time zone if you are living in Maui but your officemates are all in Chicago and you want to keep track of what time it is there.

Curious feature: If iPhone set to 24 hr time in Settings>General>Date&Time only 24hr format is allowed but if 24hr is turned off either format is allowed.