I am not aware of such plugin and did not get any result by a quick search. Could you explain more about your project.  A simple python code might do the job.  

I know python or any other code can be used, I use MATLAB to do it now. But I have to extract data out of ABAQUS and feed it to FFT code. There is a plugin like Signal Processing for ABAQUS (http://www.critical-materials.com/en/products/spa) but it's commercial and not for free use. I assume there is no open source plugin. 

There used to be one but the site is long gone. Abaqus python contains numpy which can do fft. You can use python scripting to read your signal curve, perform the fft using numpy and create a new curve, ie amplitude vs frequency, for plotting in abaqus.