At one time I was rather heavily involved in the original Linux ports of
the NoTAM software. I've worked quite a lot with Ceres, Mix, Bio, and
the others linked in Anders' message.
Kjetil's current version of Ceres appears to have consolidated most of
the goodies found in previous ports.
Btw, I've used Ceres for some noise reduction, just getting rid of some
obhvious artifacts. Most of the time I've used it as a sound creation
utility, its Transforms are certainly some of the weirdest I've used. :)
Thanks for the link, Anders, it's nice to see that the older NoTAM stuff
still lives on.