anti rocker is when you have smaller harder wheels in the middle so its easier to grind. its not as good for rolling around but everyone has it, just about.
ive never heard of extended rocker, but "rockered" is when your middle wheels are either bigger or stick out a bit more. its shit for everything unless you play roller hockey or something.
you may mean the way that GC frames have the middle wheels further apart, so you put special small wheels in there, so all 4 are touching the ground, and you still get a large gap to grind. its a good system.