Somewhere in the depths of a comms room at a Very Very Big Company, there's a very very old laptop running a very very old install of Slackware, which does one job - run a server that Radio-over-IP boxes connect to, so they can have their G.711 streams picked apart, some DSP applied to add or remove certain high frequency tones and generally clean up the audio, and be fired back out into another interface.

That was all made possible by Beej's Guide to Network Programming and the RBJ Biquad Cookbook, mostly.

Just a temporary bodge until the vendor got their shit together. I doubt it'll ever be replaced.