Inverse limit slender groups

Classically, an abelian group $G$ is said to be slender if every homomorphism from the countable product $\mathbb Z^{\mathbb N}\mathbb N$ to $G$ factors through the projection to some finite product $\mathbb Z^n$. Various authors have proposed generalizations to non-commutative groups; this has resulted in a plethora of similar but not completely equivalent concepts. In the first part of this work we present a unified treatment of these concepts and examine how they are related. In the second part of the paper we study slender groups in the context of co-small objects in certain categories, and give several new applications, including the proof that certain homology groups of Barratt–Milnor spaces are cotorsion groups, and a universal coefficient theorem for Čech cohomology with coefficients in a slender group.