The first slide trumpet (called the Firebird) was created with input from the great Maynard Ferguson, who also helped to create the Superbone (a trombone with valves).
Here’s Hayden Powell blazing through an improvisation on one.
Want one for yourself? I do, but they’re hard to come by. And they aren’t cheap. Here’s one on eBay if you’ve got a spare $6,500 lying around.