Check out Reaktor 5 at nativeinstruments.com. If you're wanting to build an instrument from scratch, I know of no better modular instrument package out there. Be prepared to do a lot of reading however. It took me a week just to get a sine wave out of the freaking thing. The preset instruments in it, however, are spectacular, and sort of like the combinator in Reason in that you can combine multiple modules and create your own complex instrument. Then just load it as a vst into your favorite DAW and you're good to go. Come to think of it, I should really buy that software,,,I've been using the stupid demo for about 3 weeks now. Sigh.......money money money.