Set driven key in Maya is a thing that lets you set a keyframe at either end of a desired motion or change for one or more attributes (say, like a finger curl position) and then tie that to a change in a different attribute (for instance, a slider you construct). When you move the slider, it causes the finger to curl. The finger joints would be the driven, and the slider would be the driver. What you linked looks like you could get the same functionality out of it, just in a little bit of a different way, so that's good to know about.

A proxy rig is (iirc; it's been a while so I may be using the term incorrectly) is a rig with much more complex controls than the skeleton that is actually in a figure, which can be a simple IK skeleton. The animations done with the proxy rig are then retargeted to the simpler IK skeleton. The reason I would use this sort of a setup is that some game engines do not support very complex rigs. You can make the proxy a complex as you like, even having full production level controls, like something they would use on a Hollywood film's CG sequence, and have all that control, and then bake those motions out to use on the simpler rig that gets used in the game engine. It's not -that- important, but it's something I'd put on a wishlist for features.

Of course, Carrara has a Python plugin, so the community could code some of these missing things if they really wanted to.

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