Pier is a Content Management System (CMS), it started as Smallwiki, then Smallwiki2, followed by Pier. Pier offers many features and functionality. The official site is http://www.piercms.com/, however it is somewhat dated. A better way to get started is download the latest Pharo and install Pier from Git.
After having a running Pier image, one may need to upgrade (I've been running an internal wiki for Amdocs since 2005).