Miller Puckette's PureData (PD) has become a central tools for me, both as a mechanism for constructing sound creation and manipulation routines, and as a generalized environment for building graphical interfaces for performance. PD is extremely powerful, open, and efficient...and it runs on every operating system I use (primarily Linux, OSX, and SGI IRIX). As opensource software it has the added benefit of easy distribution to performers and publishers as well as students at CEMC (Cornell Electroacoustic Music Center) looking to expand their arsenal of software tools. I recommend the "Pd-extended" distribution for users. Installers for your operating system can be found on the puredata.info download page or if you prefer the "bleeding edge, in the nightly builds archive.