Some very interesting experimental software for Mac and Windows, all free!
From the website:
“ixi audio is an experimental project concerned with the creation of digital musical instruments and environments for generative music. We are interested in the computer as a workshop for building non-conventional tools for musicians, i.e. not trying to imitate or copy the tools that we know from the world of acoustic instruments or studio technology. We currently work with open source software such as SuperCollider, ChucK and Pure Data, but our aim is to distribute our applications packaged in a way that allows everybody to use them. Simplicity and ease of use together with depth in interaction and expressive scope is the aim of our experimental music software.”