We deal with some pcf investigations mostly motivated by abelian group theory problems and deal their applications to test problems (we expect reasonably wide applications). We prove almost always the existence of aleph_omega-free abelian groups with trivial dual, i.e. no non-trivial homomorphisms to the integers. This relies on investigation of pcf; more specifically, for this we prove that almost always there are F subseteq lambda^kappa which are quite free and has black boxes. The almost always means that there are strong restrictions on cardinal arithmetic if the universe fails this, the restrictions are everywhere. Also we replace Abelian groups by R-modules, so in some sense our advantage over earlier results becomes clearer.
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