Algorithm 951: Cayley analysis of mechanism configuration spaces using CayMos: software functionalities and architecture. For a common class of two-dimensional (2D) mechanisms called 1-dof tree-decomposable linkages, we present a software package, CayMos, which uses new theoretical results from the authors [“Technical note: how the beast really moves: Cayley analysis of mechanism realization spaces using CayMos”, Comput.-Aided Des. 46, 205–210 (2014)] and the second author et al. [“Cayley configuration spaces of 1-dof tree-decomposable linkages, part I: Extreme points, continuous motion paths and minimal representations” (2011; arXiv:1112.6008); “Cayley configuration spaces of 1-dof tree-decomposable linkages, part II: Combinatorial characterization of complexity” (2011; arXiv:1112.6009)] to implement efficient algorithmic solutions for (a) meaningfully representing and visualizing the connected components in the Euclidean realization space; (b) finding a path of continuous motion between two realizations in the same connected component, with or without restricting the realization type (sometimes called orientation type); and (c) finding two “closest” realizations in different connected components.