Download of FFTW 3.3.7 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The program is included in Developer Tools. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. This free Mac application was originally created by Matteo Frigo and Steven G. Johnson.
From the developer:
FFTW is a C subroutine library for computing the discrete Fourier transform (DFT) in one or more dimensions, of arbitrary input size, and of both real and complex data (as well as of even/odd data, i.e. the discrete cosine/sine transforms or DCT/DST). Developers believe that FFTW, which is free software, should become the FFT library of choice for most applications.
You may want to check out more software for Mac, such as Objective Basic, Pleinpot or Epsilon, which might be similar to FFTW.