soft-synth :: Native Instruments Reaktor 5
Reaktor 5 is an object-oriented programming enviornment in the same style as Max/MSP or PureData. What you get is a very flexable and intuitive enviornment for building essential tools like effects processors, drum machines, synthesizers, sequencers, samplers, as well as experimental or custom tools.
In the latest version, NI has gone a step further and created a deep Core language where you have the ability to construct your own modules from scratch.
Overall, this is an invaluable tool for computer based generation and processing.