Impulse is a bit of eye candy for your desktop. It is a widget that displays a graphical spectrum analyzer on your GNOME desktop. It is written in C and Python, and uses GTK and Cairo graphics to generate the animation. The impulse library creates a pulse audio connection context that reads the output stream from pulseaudio in a thread natively, which can then be read from Python. You can instruct impulse to either output the raw stream or output the FFT of the raw stream.
Meta.Numerics is a Mono-compatible .NET library for scientific and numerical programming. It includes functionality for matrix algebra (including SVD, non-symmetric eigensystems, and sparse matrices), special functions of real and complex numbers (including Bessel functions and the complex error function), statistics and data analysis (including PCA, logistic and nonlinear regression, statistical tests, and nonuniform random deviates), and signal processing (including arbitrary-length FFTs).