Terry Roycroft has called his invention the Sealander, because it goes on sea and it goes on land. While that does not seem a very inventive name, the Sealander itself could one day be known as New Zealand's best motorised invention.
Imagine an affordable, mass-produced amphibious car that would drive at motorway speeds on land, then drive straight into the water where it can ride up 'on the plane' at jet-boat speeds. It only has to be half as popular as those ridiculous jet-ski things to be a huge success. The reason the world has never seen such a thing is not because people wouldn't want one, but because to make a viable commercial amphibian like this you must solve some very difficult engineering design problems.
If you have ever sat behind someone towing a boat to Lake Taupo at about fifty km/h on the Desert Road then like me you'll be saying 'please please be a success!!!'