SiON SoundObject Quartet: On Line Sequencer

SiON Found Here

Not fancy but works quite well.

 

Zach Poff: Great Collection of Free Audio and Video Software (OSX)

Press Here To Enter The Site: Zach Poff

This is a fine collection of very useful audio and video software.  My recent favorite is FrameSubtractor:

With just a little experimentation I was able to create some interesting effects such as: