  In this note we consider a notion of relative Frobenius pairs of commutative
rings $S/R$. To such a pair, we associate an $\mathbb{N}$-graded $R$-algebra
$\Pi_R(S)$ which has a simple description and coincides with the preprojective
algebra of a quiver with a single central node and several outgoing edges in
the split case. If the rank of $S$ over $R$ is 4 and $R$ is noetherian, we
prove that $\Pi_R(S)$ is itself noetherian and finite over its center and that
each $\Pi_R(S)_d$ is finitely generated projective. We also prove that
$\Pi_R(S)$ is of finite global dimension if $R$ and $S$ are regular.
