Clock is Google's official clock app. It has a beautiful Material Design interface and lets you do much more than just look at the time.
Besides the clock face itself, Clock offers many other features. The most useful is the alarm, which lets you choose which days you want it to repeat, what sound you want to use, if you want the volume to rise or not, etc.
Two other interesting features – although not quite as useful – are the timer and stopwatch. The first gives you a countdown and the second transforms your mobile into a proper chronometer that can save the times you log.
Clock also has several widgets that you can place on your Android's home screen. You can use the digital or analog version and obviously change the size of the widget to adjust it to your needs.
Clock is an excellent time app. It has almost everything an Android user could want, all presented on a beautiful Material Design interface.