I just released version 0.8 of FreeSRS, see
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The new version of FreeSRS was extented by a C++ library, which was added to the small library of Python and Fortran77 files. FreeSRS calculates the shock response spectrum (SRS) of an acceleration signal. The algorithm used is from David O. Smallwood, see "An improved recursive formula for calculating shock reponse spectra. Shock and Vibration Bulletin, No. 51, May 1981". I'm looking forward to your comments! The library is free software (GPL), have fun!