Uber Black is the only service that is (for now) allowed in Italy. It currently operates in Rome and Milan only.
These are not private citizens using their car, like the typical Uber service.
Uber Black is a black luxury limo service driven by licensed professional drivers.
Prices tend to be more expensive than regular taxis, but you also have a more luxury service aboard Mercedes type luxury cars.
But regular Taxi cars in Italy are not as old and run down as I typically see in America however, since cars can't be older than 4 or 5 years in practically all municipalities.
Uber Water taxi in Venice might be difficult to implement as there are restrictions to the navigation to private boats. The ZTL applies to the Grand Canal in Venice too.