  We discuss some testable predictions of a non-supersymmetric $SO(10)$ model
supplemented by a Peccei-Quinn symmetry. We utilize a symmetry breaking pattern
of $SO(10)$ that yields unification of the Standard Model gauge couplings, with
the unification scale also linked to inflation driven by an $SO(10)$ singlet
scalar field with a Coleman-Weinberg potential. Proton decay mediated by the
superheavy gauge bosons may be observable at the proposed Hyper-Kamiokande
experiment. Due to an unbroken $Z_2$ gauge symmetry from $SO(10)$, the model
predicts the presence of a stable intermediate mass fermion which, together
with the axion, provides the desired relic abundance of dark matter. The model
also predicts the presence of intermediate scale topologically stable monopoles
and strings that survive inflation. The monopoles may be present in the
Universe at an observable level. We estimate the stochastic gravitational wave
background emitted by the strings and show that it should be testable in a
number of planned and proposed space and land based experiments. Finally, we
show how the observed baryon asymmetry in the Universe is realized via
non-thermal leptogenesis.
