  For any right-angled Artin group $A_{\Gamma}$ we construct a
finite-dimensional space $\mathcal{O}_{\Gamma}$ on which the group
$\text{Out}(A_{\Gamma})$ of outer automorphisms of $A_{\Gamma}$ acts with
finite point stabilizers. We prove that $\mathcal{O}_{\Gamma}$ is contractible,
so that the quotient is a rational classifying space for
$\text{Out}(A_{\Gamma})$. The space $\mathcal{O}_{\Gamma}$ blends features of
the symmetric space of lattices in $\mathbb{R}^n$ with those of Outer space for
the free group $F_n$. Points in $\mathcal{O}_{\Gamma}$ are locally CAT(0)
metric spaces that are homeomorphic (but not isometric) to certain locally
CAT(0) cube complexes, marked by an isomorphism of their fundamental group with
$A_{\Gamma}$.
