To make legs for my puppet which I could control from the bottom to make them walk and also open its legs to squat and so on, I really needed a joint with exactly two degrees of freedom. An old desk wheel was the solution - by swivelling on its pivot, it allows the legs to go up and down, while the wheel motion allows it to turn outwards. Because it's constrained from rotating on the other axis, the knees don't flop over to sides when I lift them up.
I don't seem to have got a good photograph of it at the time, so the messiness here is largely the result of it lying on my roof for about a year - there was a lot more paint and stuff before! That said, I didn't feel the need to make it look terribly neat, since it was mainly intended to be seen at night, from a distance.