Say you're running late for a business meeting, and your coworkers want to know exactly where you are. Glympse is free app that lets you share your location for an amount of time that you specify. You send a "Glympse" of your location to a recipient (using the person's phone number), and he or she can see your location in real time on a map.
One cool thing about Glympse is that recipients don't have to download an app to use the service. Rather, they receive your notifications on a mobile phone or PC, and then click on a Web link to find you. Of course, you could call or text while driving, but that's often unsafe--and even illegal, depending on where you live.