PVC pipe and PVC joints are handy for making stuff. But the types of
joints that exist seem to be limited to corner joints, T joints, 4 way
joins (shaped like a plus), and 3 way corner joints (the only type of
joint that actually goes into the 3rd dimension).

Are there other types of joints? In particular, a 6 way joint would be
handy. If not, are there good alternatives to using pvc pipe where
there are more types of joints?

Also, Home Depot's smallest PVC size is 1/2" (which for some reason
isn't actually 1/2". It's .84" in diameter on the outside and .62"
inside.) I would like a size that's the same as the frame pipes of the
Chaos World of Motion set (see ChaosToy.com). Those pipes are .75"
diameter outside and .63" inside. Chaos sets are expensive and the
pipes aren't long enough, so it would be nice to get pvc pipe (or
something similar) that's the same size. I suppose I could get wooden
rods if they come in that size, but one of the niceties of pvc pipe is
the easy connection of things using the joints. If I use wooden rods
then I'd have to use nails to connect things.