Last year I released a PowerShell module called PSClock. The module contains a command to create a transparent WPF form displaying a clock. Shortly after, someone posted a request for a countdown timer. Not an unreasonable request and one I finally got around to implementing. However, I already had a module with a number of timer and countdown-related commands called PSTimers I had been thinking of a WPF-based timer, so this solved two problems.
Read on to see how it works.