In terms of other similar things to MAX/MSP (a visual audio programming interface, among other things), here's one for unix-likes, I believe (never used it, anyone know how good it is?)
The audio engine imparts a very specific sound upon everything that comes out of it, much like Max/MSP.
It was developed by one of the original Max/MSP authors. I think it was released after they left cycling74 amidst some sort of drama, but don't quote me on that.
David Zicarelli's Cycling74 maintains the original Max tree, though their contribution far exceeds "maintenance". Puckette's pd is a rewrite of Max intended to transcend some architectural limitations; as its name suggests, its conception of "data" is more fully abstracted away from the C underpinnings still visible in Max/MSP. In my opinion, pd is a more mature architecture while Max is a more mature product.
As far as I know, the only drama in the timeline revolves around Opcode (particularly its sale to Gibson), which led Zicarelli to start Cycling74. Beyond that, my impression is of mutual respect.
The tradeoff between maturity and elegance is sometimes maddening, but both are worth exploring. Max has a 30-day trial and pd is gratis/libre.
Some development history, including detail possibly of interest to hackers: http://xavier.amatriain.net/Thesis/html/node77.html Miller Puckette: http://crca.ucsd.edu/~msp/ Max Mathews: http://en.wikipedia.org/wiki/Max_Mathews pure-data: http://puredata.info/ Max/MSP/Jitter: http://cycling74.com/
Unfortunately it's windows only. It does have a lot of advanced capabilities you don't see in similar tools though, such as proper GUI elements and one-click VST export.