Views are used to define the main content of a page (ie. a list of discussions, a user profile, etc), but what about all of the other supplementary elements on a page? How does Garden handle adding buttons, menus, and all of the sundry elements that make any page complete? Modules.
Modules are extremely simple classes that have one purpose: return a string. That string can really be anything you want, but typically it will be a string of xhtml that is to be added to any of the asset containers defined in the master view.
Garden comes with a number of predefined modules, such as:
HeadModule: Allows the addition of tags to the head of the document, like link (css) tags, script tags, meta tags, etc.
MenuModule: Used to build a hierarchical menu that can then be manipulated to do a number of different tasks. For example, it is used for the main menu of Garden that includes hover-driven dropdown items, and it also is used for the main settings page as a sidebar menu.
EditInPlaceModule: Can be added to any page in the sidebars, header, or footer and allows administrators to put anything they want into that page by editing the content block in-place.