Apache Cocoon is a web development framework built around the concepts of separation of concerns and component-based web development.
Cocoon implements these concepts around the notion of 'component pipelines', each component on the pipeline specializing on a particular operation. This makes it possible to use a Lego(tm)-like approach in building web solutions, hooking together components into pipelines without any required programming.
Cocoon is "web glue for your web application development needs". It is a glue that keeps concerns separate and allows parallel evolution of all aspects of a web application, improving development pace and reducing the chance of conflicts.
The Apache Cocoon Project is the open source community project developing Apache Cocoon and Cocoon-based application frameworks. With strong foundations in XML-based server-side web application frameworks, the Apache Cocoon Project consists of a group of people that share common values on collaboration-intensive and community-based quality open source development. The Apache Cocoon Project is proud to share these values with its parent organization: The Apache Software Foundation.
The Apache Cocoon project currently consists of Apache Cocoon itself. The Lenya CMS, which is now a top-level project, started its life at Apache as an incubating Cocoon subproject.
The related projects section also lists a number of Cocoon-related projects and resources.
The documentation is located in each module and on the website under each specific Cocoon version. There is also the community effort to maintain the extensive Cocoon Wiki.