Hydraulic Coasters are all the rage these days, as they seem to be popping up everywhere. It has to be said that a coaster type hasn't been this successful and crowd-pleasing since the B&M Inverted Coaster in the early 90's.
The Original
Intamin Rocket Coaster
When Knott's Berry Farm announced Xcelerator, the amusement industry's jaws dropped. Standing over 200ft tall, with a launch speed of over 80mph in under 3 seconds, Xcelerator was to spark a launched coaster revolution. These days, inversions can be included if a park desires them. It is also known as an Accelerator Coaster.
Variations
Vekoma Motorbike Coaster
Vekoma's Motorbike Coaster, while utilizing a hydraulic launch, offers a very different ride experience from the Intamin designs. The Motorbike Coaster's cars have seats that are shaped like motorbikes, and allow riders to sit in "motorcylce riding position" as they ride through the track. Not nearly as tall or as fast as the Intamin Rocket coasters, the Motorbike Coaster, with its layout of highly-banked helixes and airtime hills, is marketed as a family attraction and is an excellent way to introduce children to launched rides.