A free app for Android, by UK Tch.

Always on Display is a handy utility for displaying a clock on the screen. It will work on any device with an AMOLED screen, even on those with multiple resolutions, such as the latest Android devices.

It displays a digital or analog clock depending on the resolution of your screen. It also supports both edge and corner lighting effects. The app also allows you to set it as a live wallpaper or live screen saver.

You can choose between two modes: Always on Display or Only on Edge.

The app also includes a notification system so you can get alerts on your phone.