QuaCa is an extensible library facilitating the computation of steady-state atom-surface quantum friction. Due to its modular domain-driven structure, QuaCa can be of further use to calculate relevant quantities that are often needed in the context of electromagnetic dispersion forces. Quantum (or Casimir) friction is a quantum-optical fluctuation-induced force that occurs in dynamical nonequilibrium, i.e. when a number of bodies are moving relative to one another (Pendry, 1997; Scheel & Buhmann, 2009). The frictional interaction between the moving system of interest and its environment is mediated by the (material-modified) quantum vacuum and persists even at zero temperature. At finite temperatures, thermal fluctuations can modify the interaction and quantum friction can be connected to the Einstein-Hopf effect (Einstein & Hopf, 1910; Ford et al., 1985; Milonni, 1981; Mkrtchian et al., 2003; Oelschläger et al., 20212). For a comprehensive review of quantum friction in various contexts as well as related effects in dynamical nonequilibrium, we refer, for example, to the reviews in Refs. (Dedkov & Kyasov, 2017; Reiche et al., 2022; Volokitin & Persson, 2007) and the references therein.