Actually, multiple tonguing - especially double - is possible on a variety of wind instruments besides just trumpet and other brass. For flautists and piccolo players, the technique is near-essential. To compare the speed of the notes, try saying "tuh tuh tuh" repeatedly as fast as you can for a while. Now switch to a "tuh-kuh." Feel the difference? For a neat effect not possible on most woodwinds (at least I've never heard it used on any others!), flute players can also produce an effect known as butterfly tonguing by rolling their tongues - this produces a "buzzing" tone, something like an insect flying by, and is often heard on Jethro Tull albums.

Other instruments compatible with double and triple tonguing that don't require it as often include clarinets, saxophones, and even oboes and bassoons (or so my bassoon professor tells me... I haven't worked on the technique too much due to the high cost of reeds.)