i agree with topolino and lykwydchykyn.
you've got to be really careful bantering a word like 'experimental' around. some people think radiohead is experimental. some people think squarepusher is experimental. hell, someone once told me he thought jeff buckley was experimental. is john fahey experimental? And then, on the other hand, I'll bet that people like Arnold Schoenberg and Karlheinz Stockhausen would flat out deny that anything they wrote was 'experimental'. Certainly, it was NEW.
I'd have to say that there's a difference in music that is intuitively original, and music that is a result of a considered and planned experiment. And, probably, the stuff that becomes popular is a great combination of the two, i.e. intuitive experiments.
But to answer your original question: No. There is no software for making experimental music. That would sort of defeat the purpose, wouldn't it? The experiment occurs to you in your head and you need to actualise it in some way. I play around with midi systems (mostly in Logic Audio), and I play around with audio manipulation (mostly with Cool Edit Pro 2/Adobe Audition), and I play around with writing for real instruments. I'm probably going to write some (simple) software this year that will do things for me. I play around with compositional principles. And I combine all of the above. There's simply no software that does this.
Though, check out a piece of software call MAX/MSP. Graphic interface stuff, pretty cool and a lot of people use it for making electronica.
(BTW, I'm one of those university kids, so, actually, all of this might be coming from the wrong angle for you. You haven't specified what YOU mean by experimental music. If you give us some examples of artists you're thinking of, perhaps we can give more feedback?)