Google Maps can tell you your speed; it has an inbuild speedometer, which is only currently available for Android users. It is on by default, but to make sure it is on, go to settings → navigation settings, and under the driving options menu, there will be a slider for it. It is useful as it will change color if you are exceeding the limit — so you don’t have to take your eyes off the road. You can also report speed cameras and traps — but only if you’re in navigation mode. Read more