A really cool device which allows ships to travel anywhere in the universe.  When activated, they simultaneously occupy every single point in the universe, and can then "select" the point they wish to remain occupying when shut off again.

Derives its improbability from a cup of tea.  Much simpler than using dilithium crystals and antimatter.

Used in the ship HeartOfGold.

Created by DouglasAdams in his HitchhikersGuideToTheGalaxy series.