AcouSTO is a linear acoustics solver based on a Boundary Element Method (BEM) solution of the Kirchhoff-Helmholtz Integral Equation (KHIE). The code is written in C, and includes an MPI-based preliminary parallelization scheme. Plan wave scattered by a unit sphere. An (extended) FORTRAN version of this code has been used for years in the authors' research group, and has reached a remarkable level of reliability. The numerical formulation has been well assessed, as the large number of scientific papers produced throughout the years demonstrates.