Jack OS X – a Jack implementation for Mac OS X: — just updated to work with Leopard. Or rather, the updates which make it work with Leopard are just now out of beta and on the front page. I took it for a spin this morning and routed a streaming story from NPR’s Flash player into Audacity, so I could make an MP3 of it. Spiffo! You gotta read the documentation though, it’s not super intuitive.
Jack is awesome. Jack is Free Software, originally developed for Linux. Yet when I actually use Linux, I never even try to use Jack, because Linux sound is so fragile in the first place that adding another possible point of failure to the mix seems downright foolhardy.