Let $\mathbf{FSet}$ denote the category of finite sets.
If we consider $\mathbf{FSet}^\text{op}$ as a Lawvere theory, we recover the category $\mathbf{Set}$ of sets as its models. If, instead, we take as our theory $\mathbf{FSet}$ itself (this is not a Lawvere theory now I think, but it still is an algebraic theory), what is the category of models?
$\mathbf{Set}^\text{op}$ is equivalent (by taking power sets) to the category of complete, atomic Boolean algebras.
In particular, $\mathbf{FinSet}^\text{op}$ is equivalent to the category of finite boolean algebras.
nLab has a page on FinSet. (and also on CABAs)