Re: AC generators and AC voltage.
AC generator's need slip rings. A commutator wouldn't work at all for AC because of the direction required for the current.
Yes there is AC Voltage. This is called continuous/analog voltage and has many applications.
AC Voltage can be expressed as a curved graph of v (y-axis) vs t (x-axis). Any sinusoidal type graph or continuous graph of v vs t is showing AC voltage. So in fact the AC generator's output voltage is AC Voltage.
DC voltage is just a constant voltage which does not vary with time. It is a straight horizontal line on the graph v vs t.
Source EE.