Clocks - A minimal world clock app for your Mac's menubar
Mountie - Mount a second screen (iPad/iPhone/tablet) to your MacBook
Clocker - Keep track of people in different time zones
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.
144blocks - Colorful way to track your time! Inspired by Wait But Why
Luna Display - Hardware that turns the iPad into a wireless second display