Synthedit... hrm. It's sorta like PD or Max... or Reaktor... I'm way more familiar with PD and Reaktor and they seem more powerful. Creating VSTs would be cool, but you can run through Reaktor as a VST in a pinch (just can't make a standalone plugin out of it).

CSound is not that bad (it runs great on osx too). It does some things in a way that is superlogical for streams processing, and is probably my favorite of all the non-realtime code sorta type thingies out there. If I want a sound that's like a swarm of bees or a superphat string sound, it's probably quicker in CSound than anything else (all patches are polyphonic by default... whereas polyphony is harder to manage in max/msp). If it seems like you can't get your head around it, check out The CSound Book by Richard Boulanger... good stuff, with a sensible article by article approach. Nerdier than Max, but not by much... I found it way easier to understand than Supercollider.

yeah i also liked audiomulch - its a very easy interface
synth edits soundengine sounds kind of limited , but that can be my opnion....