Archetypes are altered versions of the existing 3 classes. They differ from specializations in that they have different class abilities from the get go. And unlike a specialization that builds upon the base classes abilities, the archetype abilities typically replaces some of the base class abilities.
The idea of archetypes and the original sample archetypes were created by Taylor Bland and originally posted on the Fantasy AGE G+ Community.
His Archetypes were designed to more closely mirror some of the classes in the D&D Game.