Throughout the book we have been using a plain vanilla Confluence installation without any added features or functionalities. Add-ons are separately installed components that supplement or enhance functionality in Confluence. This can vary from a single feature such as a macro to something that could be a product on its own, such as the add-on "Team Calendars".
There are over 500 add-ons for Confluence available via the Atlassian Marketplace and more are being added. These add-ons can be downloaded, evaluated, and purchased via the Marketplace. The Marketplace can be access directly via the Internet or by making use of the Universal Plugin Manager, from within the Confluence Administration Console.