  A new class of six-dimensional asymmetric orientifolds is considered where
the orientifold operation is combined with T-duality. The models are
supersymmetric in the bulk, but the cancellation of the tadpoles requires the
introduction of brane configurations that break supersymmetry. These can be
described by D7-brane anti-brane pairs, non-BPS D8-branes or D9-brane
anti-brane pairs. The transition between these different configurations and
their stability is analysed in detail.
