Zotonic is a content management system based on the functional programming language Erlang. It's an amazing product, benefiting from the concurrent nature of Erlang to perform at blazing speeds, typically 10-100 times faster than a "regular" cms built in PHP on Apache.
The data model of Zotonic is very generic and can be though of to use only 2 database tables: one to store documents, called resources, and one to create connections between these resources. Furthermore, resources are classified in a category tree, so you can develop functionality (like different page controllers and templates) based on which category a resource belongs to.
What did I build?
I am still involved as a core developer in the Zotonic team. My main responsibilities include release management, documentation and maintaining several of the core modules.