iOS: Slow Down is an app for GPS-enabled iOS devices that slows your music when you're driving faster than the speed limit, aiming to keep you moving at a safer (and more legal) speed without shifting your eyes from the road.
The concept is very simple: you launch the Slow Down app on your iPhone, iPad or iPod touch (with an added, third-party GPS) and start playing your music. You open up Slow Down, create a music playlist for your drive, and choose a speed limit. While you drive, Slow Down uses your GPS to work out how fast you're going and if you exceed your set speed limit it slows down your music. If you exceed the speed limit by more than 10km/h, your music will stop completely until you slow down.
The main disadvantage of the app is that you can only select three common speed limits: 50km/h, 90km/h and 120km/h. In future iterations it would be nice to be able to set the speed limit on a slider, rather than choosing presets, and support for other units of measurement wouldn't be too bad either. Nonetheless, if you're looking to keep an eye on your speed without actually keeping an eye on it, Slow Down can help you do that.
Slow Down is a free app and it's available right now in the iTunes App Store.