What are DotNetNuke Modules?
"Modules" are modular pieces of code that each present some functionality to the user. Popular modules include user forums, photo galleries, blog publishers, directory tools, chat applications, contact managers, and events calendars.
In typical use cases, several modules will be grouped together to create a webpage or intranet page. These modules can easily be added, edited, deleted, restored, moved within a tab, or transfer to another page.
Within the DotNetNuke ecosystem, there are a wide variety of developers continually producing new and exciting modules for the DotNetNuke application framework. These module developers often build modules which they will sell on their sites or through marketplaces or reseller stores (some offer modules for free.) Developers will often offer up their services to design custom modules for their clients.

In addition to the so-called "commercially" developed modules on the market, there are also DotNetNuke modules currently being developed by DotNetNuke Project teams. These modules are offered similarly to the DotNetNuke application itself, licensed under open source standards and offered free to download.
List of built-in module that dnnsite offers (depending on the web solution packages seleted):
Module :: Announcements
Module :: Blog
Module :: Chat
Module :: Contacts
Module :: Documents
Module :: Events
Module :: FAQ
Module :: Feedback
Module :: Forum
Module :: Gallery
Module :: IFrame
Module :: Links
Module :: Map
Module :: Media
Module :: News
Module :: Reports
Module :: Repository
Module :: Store
Module :: Survey
Module :: Users Online
Module :: Wiki
Module :: XML