  We consider D-branes at orientifold singularities and discuss two properties
of the corresponding low energy four-dimensional effective theories which are
not shared, generically, by other Calabi-Yau singularities. The first property
is that duality cascades are finite and, unlike ordinary ones, do not require
an infinite number of degrees of freedom to be UV-completed. The second is that
orientifolds tend to stabilize runaway directions. These two properties can
have interesting implications and widen in an intriguing way the variety of
gauge theories one can describe using D-branes.
