Pd (aka Pure Data) is a real-time graphical programming environment for audio, video, and graphical processing. It is the third major branch of the family of patcher programming languages known as Max (Max/FTS, ISPW Max, Max/MSP, jMax, etc.
Pure Data vs Max/MSP opinions
The original one I used and it's open source.
VCV Rack is a modular synthesizer inspired by Eurorack systems. It acts a host for virtual modules which perform various audio processes. E.G. oscillators, filters, envelope generators, sequencers and more that can be connected freely in almost limitless combinations.
TouchDesigner is a complete authoring tool for building interactive 3D art, visualizations, prototypes and UIs. Derivative makes and supports TouchDesigner and offers their services to do custom production using TouchDesigner.
Native Instruments Reaktor is a virtual, modular synthesis platform. REAKTOR also provides a platform for modular synthesis in the form of Blocks – a range of sound generating and sound shaping modules.
openFrameworks is an open source C++ toolkit designed to assist the creative process by providing a simple and intuitive framework for experimentation. The toolkit is designed to work as a general purpose glue, and wraps together several commonly used libraries, including:
Vuo lets media creators make interactive animations, exhibits, performances, and professional-grade media projects by connecting up simple building blocks. Media creators can use these blocks to manipulate audio input, images, layers, videos, and 2D + 3D graphics, as well as...
Isadora is the award winning, interactive media presentation tool that allows you to follow your artistic impulse. Whether you are an artist, designer, performer, or VJ, you can quickly and easily harness the limitless potential of digital media and real-time interactivity with...
Orca is an Esoteric Programming Language and live-coding environment for musical experimentation. In Orca, each letter of the alphabet is an operation, lowercase letters operate on bang, uppercase letters operate each frame.