Unschoolers don't use a cirriculum. The idea of unschooling is that when you come up with something that sounds interesting enough to learn, you figure out how to learn about that subject. Go as deep or as shallow as your interest takes you. Just like in the adult world. When we started homeschooling our kids, we were using a curriculum, and the kids did it, but they were bored silly pretty quickly. We came to call this "school at home". What's the point of that? Once we embraced unschooling, our kids blossomed. The loved it. They learned so much on their own it was astonishing.
The public school methodology works great for what it was designed for. The problem is that it was designed to create good factory workers for the dawn of the industrial age. For today's world, the school system is broken, and unschoolers aren't going to wait for someone to fix it. Taking action. Taking control.
The unschooling community is very much like the open source community. It's about freedom and control of your own destiny.