A simple stopwatch / hourglass / timer that you can set to 30 seconds, 1 minute, 2 minutes, or 5 minutes, and that every Google Hangouts meeting participant can see.
It was developed to improve productivity during our remote meetings, by granting a 2-minute speaking slot to every team member.
Demo: https://www.youtube.com/watch?v=VKtM0je-CTs
More info + install: http://hangout-timer-app.appspot.com/