rsutils
Simple utility and convenience functions such as vector math, coinflipping, and ffts in C used by roughsoft.
So far these are just portable niche functions that I needed for a project that did audio DSP and 3D graphics/physics. It probably don't apply to many others, but it might be a useful reference for a free and open Fast Fourier Transform, for example. As a caveat, there are certainly lots of other libs out there that do these things better and more efficiently. That being said, I'm putting this up under the MIT license, so you can use it in your commercial projects without worry if there's something you want to use.