What Are Some Ways to Add a Countdown Timer to Microsoft PowerPoint?

For Windows PowerPoint

There’re several ways:

1. VSTO Add-in (e.g. LTC Timer S)
2. Web Add-in (e.g. LTC Timer Win)
3. Flash Timers (e.g. PPT Flash Timer)
4. Manually create timer using shapes and transitions in PowerPoint (e.g. Timers from A6 Training)
5. Write code in VBA (e.g. this tutorial)

For Mac PowerPoint

1. PPT Mac Timer

This post was originally appeared as an answer on Quora.