Mac: Sometimes, you just need a quickly accessible timer. Countdown is a Mac app that does just that.
Countdown lives in your menu bar, where you can quickly set a timer without a lot of clicking. It also respects your system alert sound settings, so if you play music through a stereo and have alerts set to your Mac's speakers, it doesn't go blaring through your sound system. It's a simple little app, but it does its job well.