Processing is an open source programming language and environment for people who want to create images, animations, and interactions and created by Casey Reas and Ben Fry.
It has been used by Architect, Graphic Designers, Jewellery makers and anyone interested in Generative processes based on simple rules with a beautiful graphical and interactive output. Below are a few examples:
First lets start with the creators of “Libraries” which are like Plugins one can add to Processing in order to use pre-determined functions such as 3D viewer or Physics. One of the most famous libraries, Toxiclibs, is developed by the self-taught designer Karsten Schmidt, director of PostSpectacular.

Above: Kartsen Schmidt’s work exhibited at the V&A as part of their Cult Of Beauty aestheticism exhibition.
N-E-R-V-O-U-S is a design studio which uses Processing to generate jewellery and furniture based on natural systems and simple laws. Thanks to an online Processing interface and Toxiclibs library, the “product” is generated according to the buyers’ wishes and then fabricated using a 3D printer. Below are images and videos of their work:

Above: Image and video of Laplacian Growth System
Above: Hele-Shaw Cell experiments with Paint and Plastic

Above: Hyphae Growth Process Diagram and Lamp Images
Biothing is an Architectural Practice led by Alisa Andrasek and Jose Sanchez, below is a project they have developed with the large scale 3D printer D-Shape based on the Turing Patterny:
Above: Turing Pavilion by Biothing using Processing
One of the AA DRL Masters team (Thiago Mundim, Sanhita Chaturvedi and Esteban Colmenares taught by Marta Malé-Alemany,Daniel Piker & Jeroen Van Ameijde), developed a revolutionary technique to knit on a building scale:
Above: the Knitectonics Project Interface, using Processing and the Toxiclibs Library