Suppliers provide information that can be used by the Reporting app.

The following table is a list of suppliers provided by Reporting.

Attachment SupplierSupplies information about attachments in Confluence.
Body SupplierSupplies information about content bodies in Confluence.
Boolean SupplierAllows some simple post-processing on Boolean values.
Class SupplierProvides information about object classes.
Collection SupplierProvides information about collections of items.
Comment SupplierSupplies information about comments attached to Pages or News Items in Confluence.
Content SupplierSupplies information about Confluence content, such as pages, news items, attachments and comments.
Date SupplierProvides information about dates.
Debug SupplierProvides access to various objects useful for debugging.
Email SupplierSupplies information about email addresses.
Expanded SupplierThis provides access to the 'expanded' object created by the Expanding Reporter macro.
Global SupplierThis supplier can be used from any context, and provides information about global values, such as the current user, the date/time, etc.
Grouped SupplierProvides access to the results of the Grouping Reporter.
Label SupplierProvides information about Confluence content labels.
Link SupplierProvides information about links coming from Confluence content.
Mail SupplierSupplies information about archived email files stored in Confluence.
Map Entry SupplierProvides access to the key and value of a specific map entry.
Map SupplierProvides information about 'Map' collections, which are collections of information with a key/value relationship.
Match SupplierThis provides access to match values using regular expressions.
News SupplierSupplies information about news items (a.k.a blog posts) in Confluence. 
Number SupplierProvides information about numbers.
Object SupplierProvides general information about any object.
Page SupplierSupplies information about Confluence pages.
Query SupplierProvides access to the query objects created by reporters such as Local ReporterContent Reporter, etc.
Report SupplierProvides access to information about the current report.
Request SupplierProvides access to the headers and parameters passed in the HTTP request for the current context.
Salesforce SupplierProvides access to any type of SalesForce object. Refer to the SalesForce Standard Objects API for a complete list of all object types as well as all available fields for each object.
Scaffold Data SupplierProvides access to data set using Scaffolding Data macros.
Session SupplierProvides access to the HTTP Session context.
Space SupplierThis supplier provides key values for Confluence Spaces.
Stats On SupplierPerforms basic statistical analysis on values in a Collection of items.
Stats SupplierProvides access to calculated statistics on a set of data.
Text SupplierProvides information about text values.
User Group SupplierProvides information about user groups.
User SupplierProvides information about Confluence Users.
Value SupplierFinds or creates specific values for use with keychains.
Variable SupplierRetrieves variables set with the Report Variable macro in the current context.

Other apps such as Linking for Confluence and Connector for Salesforce & Confluence Server & Data Center also provide their own Suppliers. See the complete list for details.