VideoProof lite combines the GPS speed from the iPhone GPS and puts the information directly onto video as you record the video. Thus providing "video proof" of the actual speed you attained while videoing yourself.
Whether you are a kitesurfer, snowboarder, skier, cyclist, or sailor and you want to take "point of view" video performing stunts or just plain going fast, then this app is for you. Combine it with a waterproof case such as Lifeproof, and attach it to GoPro attachments and you can take spectacular video of your achievements.
The application also has a heads up display showing you your metrics in realtime whether you are videoing or not, to give you that dashboard that you have always been looking for.
This makes a great dash cam for your car.
nb. the application is constrained by the metrics and accuracy of the metrics provided by the iPhone, but in normal outdoor settings this should be just what you need to impress your friends.
There is also in App Purchasing to upgrade the app to the full VideoProof app which opens up tracking and other metrics.