  We present LinearResponse.jl, an efficient, versatile public library written
in julia to compute the linear response of self-gravitating (3D spherically
symmetric) stellar spheres and (2D axisymmetric razor-thin) discs.
LinearResponse.jl can scan the whole complex frequency plane, probing unstable,
neutral and (weakly) damped modes. Given a potential model and a distribution
function, this numerical toolbox estimates the modal frequencies as well as the
shapes of individual modes. The libraries are validated against a combination
of previous results for the spherical isochrone model and Mestel discs, and new
simulations for the spherical Plummer model. Beyond linear response theory, the
realm of applications of LinearResponse.jl also extends to the kinetic theory
of self-gravitating systems through a modular interface.
