Stand-up toothbrushes are toothbrushes with an integrated Weeble Wobble (read: weighted base) at one end so they always stand up and don't collect shit particulate laying on the bathroom sink (oh it's there -- you can't see it but it's there).
Take one look at this brilliant design concept for a toothbrush, and you can see how it's a big improvement over current designs. Set it down, and its head pops upright, thanks to a weight embedded in the bottom.
The toothbrush's bulbous base fits neatly in the hand, too. It's such a good idea, it won a Red Dot Concept Award.
Impressive. But you know what would be even more impressive? If the actual brush heads were replaceable so I didn't have to buy a $10 weighted handle every time I needed a new brush. BOOM -- CONSIDER IT INVENTED! Hello, Oral-B? Transfer me to the check-writing department.