Comments on Gepner models and type I vacua in string theory

We construct open descendants of Gepner models, concentrating mainly on the six-dimensional case, where they give type I vacua with rich patterns of Chan-Paton symmetry breaking and various numbers of tensor multiplets, including zero. We also relate the models in D < 10 without open sectors, recently found by other authors, to the generalized Klein-bottle projections allowed by the crosscap constraint.