Richard Bannister release a shareware, Cacophony which is able to edit multichannel audio under X

If you need a metronome under MacOS X you can use MetroGnome a little freeware rather practical.

Apple today unveiled an all new Power Mac G4 line featuring dual PowerPC G4 processors in every model, starting at just $1,699 (US). With dual 1.25 GHz, dual 1 GHz and dual 867 MHz PowerPC G4 processors, the new Xserve high-performance architecture with support for up to 2GB of Double Data Rate (DDR) memory at up to 333 MHz, the industry's first ATI Radeon 9000 Pro graphics card and an enhanced enclosure with increased storage up to nearly half a terabyte.

GRM Tools Classic TDM 1.3.5 is now HD compatible. It is now available
for download from the GRM site. You can also request a CDROM installer by email to: mailto:grmtools@emf.org
You can use theses plug-ins for free for two weeks.
GRM Tools Classic TDM 1.3.5 is said to be (by the developpers themselves) a bundle of eight plug-ins that lets
you move sounds through space, dynamically sculpt the highs and lows
of a sound, freeze sounds in time, change a single voice into a
crowd, create unique reverberation effects, change the attack
characteristics of sounds, transpose in multiple layers, add density
and spectral resonance to your sounds, and much more. The plug-ins
are BandPass, Comb Filters, Delay 24, Doppler, Equalizer, Freezing,
Pitch Accum, and Shuffling.

If you're not familiar with these plug-ins, take a quick tour at :
http://www.grmtools.org/quicktour/

If you're looking for a new way to torture audio in real time, geometer is the one. Geometer is a visually oriented waveform geometry plugin.
Use it as an insert FX on a mono track, and explore...(you'll hear why they're called destroyFX)
It's free (but you can contribute by a donation) and you can get the plugin and its documentation on the destroyFX server.