  "Brane supersymmetry breaking" is a peculiar phenomenon that can occur in
perturbative orientifold vacua. It results from the simultaneous presence, in
the vacuum, of non-mutually BPS sets of BPS branes and orientifolds, which
leave behind a net tension and thus a runaway potential, but no tachyons. In
the simplest ten-dimensional realization, the low-lying modes combine the
closed sector of type-I supergravity with an open sector including USp(32)
gauge bosons, fermions in the antisymmetric 495 and an additional singlet
playing the role of a goldstino. We review some properties of this system and
of other non-tachyonic models in ten dimensions with broken supersymmetry, and
we illustrate some puzzles that their very existence raises, together with some
applications that they have stimulated.
