A Floorless Coaster is a type of steel roller coaster manufactured by Bolliger & Mabillard where riders sit with no floor underneath them allowing their feet to swing freely just above the track. Development of the Floorless Coaster began between 1995 and 1996 with Medusa (now known as Bizarro) at Six Flags Great Adventure opening on April 2, 1999, making it the world's first Floorless Coaster. Floorless Coasters also tend to have 3 to 7 inversions incorporated in the layout of the coaster. Recently, Bolliger & Mabillard have used floorless trains on their Dive Coasters, such as Griffon and SheiKra. Though they contain floorless trains, the coasters are still not considered Floorless Coasters as B&M classifies them as another model. Also, Maurer Söhne have designed their own version of the Floorless Coaster, a variant of their X-Car called X-Car Floorless, but currently do not have any installations.