  We study combinatorial and topological properties of the universal complexes
$X(\mathbb{F}_p^n)$ and $K(\mathbb{F}_p^n)$ whose simplices are certain
unimodular subsets of $\mathbb{F}_p^n$. We calculate their $\mathbf f$-vectors
and their Tor-algebras, show that they are shellable but not shifted, and find
their applications in toric topology and number theory. We showed that the
Lusternick-Schnirelmann category of the moment angle complex of
$X(\mathbb{F}_p^n)$ is $n$, provided $p$ is an odd prime, and the
Lusternick-Schnirelmann category of the moment angle complex of
$K(\mathbb{F}_p^n)$ is $[\frac n 2]$. Based on the universal complexes, we
introduce the Buchstaber invariant $s_p$ for a prime number $p$.
