  We discuss the construction of chiral four dimensional ${\bf T^6/(Z_3 \times
Z_3)}$ orientifold compactifications of IIA theory, using D6-branes
intersecting at angles and not aligned with the orientifold O6 planes.
Cancellation of mixed U(1) anomalies requires the presence of a generalized
Green-Schwarz mechanism mediated by RR partners of closed string untwisted
moduli. In this respect we describe the appearance of three quark and lepton
family $SU(3)_C \times SU(2)_L \times U(1)_Y$ non-supersymmetric orientifold
models with only the massless spectrum of the SM at low energy that can have
either no exotics present and three families of $\nu_R$'s (A$^{\prime}$-model
class) or the massless fermion spectrum of the N=1 SM with a small number of
massive non-chiral colour exotics and in one case with extra families of
$\nu_R$'s (B$^{\prime}$-model class). Moreover we discuss the construction of
SU(5), flipped SU(5) and Pati-Salam $SU(4)_c \times SU(2)_L \times SU(2)_R$
GUTS - the latter also derived from adjoint breaking - with only the SM at low
energy. Some phenomenological features of these models are also briefly
discussed. All models are constructed with the Weinberg angle to be 3/8 at the
string scale.
