The linuxCNC project[1] is a distribution based on the real time kernel extensions for debian for real time cnc machine control. It used to be possible to get few-us guaranteed latency, but with modern multicore machines you are stuck with about 100us due to the way the caching works. Still plenty fast enough for audio!

[1] http://linuxcnc.org/

I thought you wanted it for yourself, though?

If you wanted something that lots of other people could use, in principle you could make your own Linux distribution with a particular set of patches.

Good point, I've been down that rabbit hole myself.