HUD for Auto's
 

Just came across this product:

http://www.gearbest.com/obd-diagnost...ampaign=FB1511

For $30 seems like some affordable tinkering...

I've built some simple phone apps that work on the same principle - displaying a mirror image which then reflects off the windshield. It's simple in principle, but in practice it doesn't work very well because the reflected image is not focused at infinity. Your focus must shift from what you're looking outside to the reflection and back again.

Something like this has the right optics and approach, but it's more expensive of course.

Navdy looks nice, but...
 

it currently does not support tablets. I think this unit would be pretty useful if it could display ForeFlight, or some such program, but the options appear limitless. I do not think that the cost of the unit is unreasonable, either.