  String theory is the leading contemporary framework to explore the synthesis
of quantum mechanics with gravity. String phenomenology aims to study string
theory while maintaining contact with observational data. The fermionic
$Z_2\times Z_2$ orbifold provides a case study that yielded a rich space of
phenomenological models. String theory in ten dimensions gives rise to
non--supersymmetric tachyonic vacua that may serve as good starting points for
the construction of phenomenologically viable models. I discuss an example of
such a three generation standard--like model in which all the moduli, aside
from the dilaton, are frozen. The M\"obius symmetry may turn out to play a
central role in the synthesis of quantum mechanics and gravity. In a local
version it plays a central role in string theory. In a global version it
underlies the Equivalence Postulate of Quantum Mechanics (EPOQM) formalism,
which implies that spatial space is compact. It was recently proposed that
evidence that the universe is closed exists in the Cosmic Microwave Background
Radiation \cite{DiVMS}.
