OS X's CoreAudio is still an incredibly well-designed technical architecture, designed by a team who really understood digital clocking from a hardware perspective and the importance of low-latency kernel support. It's still kind of amazing to me that it was essentially fully baked by 2002-2003. On Windows there's now WASAPI Event, which has a similar architecture, but for the longest time third-parties had to step in with a third party solution (ASIO) because the OS support wasn't there (and ASIO really only solves a subset of the problems CoreAudio solves). I'm frustrated by how little attention the driver and documentation side of things has gotten from Apple since then, but for some specialized requirements the underlying architecture is still just fantastic.