Water-jet machines are a special class of CNCs which use highly pressurized jets of a mixture of water and powdered abrasive, such as garnet. This can be assumed to be similar to Laser Cutters. They can only cut objects in 2 dimensions. However, unlike a laser cutter, the water-jet can cut through thick metals like steel, aluminum, and even carbon nano-fiber sheets!
Here is an example of a circular disc I cut from a steel slab for a funny little project, which uses the delrin from a previous post.
Here is another example of water-jet cutting to make a keychain.