The software to get around the GCD comment is what they usually use when you program delays into macros (such as you can do with the G15) so that it casts as soon as the GCD ends by itself. Some also do this with a macro that repeats the keypress for the length of the GCD exactly, so that it will always cast once, as soon as possible, whenever during the GCD you press the button. (ie gcdgcdgcdgcdCASTWORKSgcdgcd and the cast can be anywhere in that snippet - it will go off ASAP and the gcd eats the rest)
It's not so much having no GCD, as being able to cast and let it wait the GCD out itself, without timing your key presses.
If that's what they meant then it is something easy to do, does qualify as botting/automation in many blue answers, and isn't doing anything that the server would prevent itself.