We can separate this discussion into two categories:
1. ANY car (this includes kit cars, race cars converted for the roads, etc
2. any factory production car from a major auto manufacturer.
maybe the requirements aren't any different, but at a glance it seems like kit cars can get away with a lot less to be street legal than a full factory production cars (for example 5 mph crash bumpers and such)
i tried looking online, but dont really know the right keywords to find the right site with the laws and a definite list.
but i figure it has to do with things like:
turn signals, brake lights, side reflectors, rear view mirrors, headlights, etc.
anyone know where the laws on this are clearly spelled out and wether its standard across all 50 states or varies from state to state?