Is there a way to lock an axis for a joint? E.g. a joint that cannot rotate along the Z axis or something?
I'm not meaning on a per-transform basis.

What for when you could lock every transform you make? Well, for one it's cleaner (since you won't even accidentally rotate the joint wrong and someone else wouldn't do so, either) and for another any constraints would have to obey. And it's just quicker than going into axis-constrained transform every time you move that joint.

Good question, I asked a similar question on elYsiun http://www.elysiun.com/forum/viewtopic.php?t=37782 but no one has replied. I tried adding a key's for the axis I wanted to lock set to zero streched over the duration of the animation. But it doesn't work well, you can only add key's to all of the axis at once, so you keep editing the curves.