State of Hard Disk Recording in Linux?

Madfishmonger asks: "I'm putting together a live computer rig for a band to play back backing tracks as well as simultaneously transmit MIDI program and control changes to various synthesizers and digital mixers. Are there any Linux-based apps (especially Linux PPC ^? , since we'll be running an older PowerBook) which can replace software like Logic, Cubase and ProTools for simpler tasks like managing MIDI ^? program changes and audio playback simultaneously, or which are even capable of rudimentary hard disk recording tasks, and will also work with the more common multi-IO MIDI interfaces from makers like MOTU and Emagic? I haven't heard of anything comparable to the current Mac and Windows-based technologies like TDM ^? , VST ^? , RTAS and ASIO, but is there anything in the works which could give the music community a third platform to work on, or do I have to wait for the big name proggies to come out on OS X?"