Instead of classes, Ersatz uses archetypes to capture closely related abilites. An archetype is made up of a small to moderate sized grouping of features, powers, resources and sometimes even ability scores that work well together.
In a setting where the characters have levels, the archetypes take the place of a class. However, a given character may have multiple archetypes rather than having a single class as is most class systems.
In a setting where the characters use a point buy system, taking an archetype is generally 10-20% cheaper than taking the features, powers and resources separately. If, while progressing a character piecemeal, you purchase all of an archetype’s traits, you can retroactively receive the archetype’s cost reduction.