Supposedly the Norwegian Forest Cat is the only breed of small cat that climbs down trees headfirst, although it's usually said to be more the controlled fall thing the other poster says -- they just run down and manage not to crash at the bottom. But the first hit on YouTube for 'Norwegian Forest Cat climb down tree headfirst' shows one making its way down at a fairly leisurely pace:

https://www.youtube.com/watch?v=3Izq1hMUPvY

For other breeds they say the shape of the toes/claws forces the cat to go forwards, but somehow Norwegian Forest Cats just have exceptionally strong claws and forepaws that let them do the job. That always sounded weird to me, though; their claws and arms don't look that different from other cats. Surely it's just a quirk from the breeding program?