Diretamente do site:
Processing is an open source programming language and environment for people who want to program images, animation, and sound. It is used by students, artists, designers, architects, researchers, and hobbyists for learning, prototyping, and production.
Uma aplicação:
http://www.solaas.com.ar/dreamlines/index.htm
Mais aplicações:
http://www.processing.org/exhibition/index.html