Fliqlo Screensaver - A screensaver that displays the time using a flip clock.
Duet Display - With Duet Display, you can transform your iPhone or iPad into a second display to expand the screen space of your PC or Mac system.
Padbury Clock Screensaver - Minimal screensaver for Mac
Luna Display - Hardware that turns the iPad into a wireless second display
Clock Screen Saver - Clock Screen Saver is a free cool looking screen saver that displays the current time in the way of digital or analog clock faces.
iDisplay - iDisplay is an app that turns a mobile device into a secondary desktop monitor. The app currently supports iOS, Android, Windows and MacOS, and it lets users connect a desktop computer to a mobile device over WiFi. Read more about iDisplay.