FerFT is a multi-purpose spectral analyzer based on the successive Fourier transformation method. It features an input signal monitor which can sample input signals through a microphone with various sample rates and show them graphically on the panel. It also lets you calculate power spectra successively along with sampled input signals and show them graphically on the panel. Finally, it provides a filter to modify spectra and regenerate signals from them.
URL: FerFT: Spectral Analyzer