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.
Swipe the digits to change background color to bright red to use as a night flashlight. Swipe digits again to get back to black blackground (and old brightness).
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.
AutoLock is turned off in the app so the clock continues to display during the night but with v1.80 and up if the phone is unplugged or power is lost then the display will turn off after the number of minutes set in the AutoLock feature. If AutoLock is set to never then the display will stay on but at the lowest power consumption setting. A 1/2 full battery icon is displayed if battery is being drained (see screenshot for largest iPhone).
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.