  Let $\text{Gprj}\mbox{-}\Lambda$ denote the category of Gorenstein projective
modules over an Artin algebra $\Lambda$ and the category $\text{mod}\mbox{-}
(\underline{\text{Gprj}}\mbox{-}\Lambda)$ of finitely presented functors over
the stable category $\underline{\text{Gprj}}\mbox{-}\Lambda$. In this paper, we
study those algebras $\Lambda$ with $\text{mod}\mbox{-}
(\underline{\text{Gprj}}\mbox{-}\Lambda)$ to be a semisimple abelian category,
and called $\Omega_{\mathcal{G}}$-algebras. The class of
$\Omega_{\mathcal{G}}$-algebras contains important classes of algebras,
including gentle algebras. Over an $\Omega_{\mathcal{G}}$-algebra $\Lambda$,
the structure of the almost split sequences in the morphism categories
$\text{H}(\text{Gprj}\mbox{-}\Lambda)$ and the monomorphism categories
$\mathcal{S}(\text{Gprj}\mbox{-}\Lambda)$ of $\text{Gprj}\mbox{-}\Lambda$ is
investigated. Among other applications, we provide some results for the
Cohen-Macaulay Auslander algebras of $\Omega_{\mathcal{G}}$-algebras.
