This paper presents a survey of active truss modules (ATMs) which can be used to construct modular, long-reach, lightweight truss-based manipulators (TBMs). Theoretical classification is presented for candidate ATM geometries. A survey of the literature is presented to subjectively compare practical modules which have been proposed. Kinematically-equivalent serial analogies are given for each of the in-parallel-actuated ATMs; use of these analogies can simplify TBM control. The intent of this paper is to present ATM alternatives and discuss subjective criteria for design selection, rather than to choose one best module.