This is a HUD display i built a while ago. It works on the concept that the windshield glass reflects some of the light from the phone's display while letting through some of it. So we have a good transparent projection over the windshield. But since it is a reflection, it will be mirrored/flipped.
There are few navigation apps out there which can output a mirrored view, so that it gets corrected once projected.
Having used one such app for a while, i started missing google maps. Only option i could think of to use GMaps is to mirror the entire phone's display. And having bought a new phone recently :P, i thought i could root my old one and play with it.
Apparently it turns out that there are no such options / mods or custom roms available for doing this. So thought of doing it myself. And this is the custom rom rebuilt from android's source to include HUD mode