I roughly followed the design for two connected universal joints described in Making Mechanical Marvels in Wood. It doesn’t serve any purpose at all except to amuse me for a few minutes if I’m bored! Further reading on universal joints if you’re really bored can be found on Wikipedia and Belden Universal.
Some other wooden universal joints in include Wood U-Joint Construction and The Universal Joint – A Working Wood Model (which comes from a design in Making Wooden Mechanical Models)