I want to concrete "stain" my garage floor. (No epoxy coats - ugly.) Does this surface hold up to parked cars?

yes a concrete stain should hold up to cars. The stain actually "stains" your concrete about a quarter of an inch deep and colors the concrete the color of the stain. The only way to ruin the stain is to chip the concrete. But make sure you really like the color of stain you chose because there is no easy way to remove it besides breaking out the concrete and replacing it.