The Freerider buggy board from Mountain Buggy is one of the coolest stroller accessories around. It's a kids scooter that not only attaches to back of many strollers, it is also a freestanding scooter by itself. And here is our first celebrity spotting: Liev Schreiber was seen out and about with his two boys in NYC yesterday. While Samuel rides in a Mountain Buggy stroller, Sasha rides on the back with a freerider.