FFT is a project mainly written in ..., it's free.
FFT library for Nimrod
This module implements discrete Fourier transforms.
Computes the FFT and inverse FFT of a length N complex sequence. This is a rather simplistic, bare-bones implementation that uses recursion rather than looping. It runs in O(N log N) time but is not the fastest of algorithms. Some simple optimizations have been made, but speed is not the main goal.
requires that N is a power of 2
not the most memory efficient algorithm (returns a new vector rather than performing it in place)