Semantic MediaWiki is an extension for managing structured data in your wiki and for querying that data to create dynamic representations: tables, timelines, maps, lists, etc. The actual homepage of Semantic MediaWiki, including user documentation in multiple languages, is semantic-mediawiki.org. There are various other pages in the MediaWiki and Wikipedia space related to SMW, but the homepage is the most up-to-date source of information.
There are a large number of "spinoff" extensions that require the presence of Semantic MediaWiki; see the category Semantic MediaWiki extensions for the full list (some of these extensions are obsolete).
The instructions are located on the help page about the installation.
- Semantic MediaWiki homepage
- Semantic MediaWiki article on Wikipedia
- Historical Semantic MediaWiki documents on meta.wikimedia, describing the genesis of the project and its early design
- The Semantic MediaWiki Community Wiki, which features its own list of sites that use SMW, filterable by language, data type, etc.
See also 
- Wikidata - a project to get similar functionality onto Wikipedia
- Semantic Bundle - a bundle of SMW-related extensions
- Similar extensions
- Extension:Wikibase+ Extension:DataValues + Extension:ValueParsers + Extension:ValueFormatters + Extension:ValueValidators (extensions used by Wikidata project to represent and manipulate with structured data)
- Extension:Data (a similar extension)
- Extension:DynamicPageList (can extract data from articles, especially template variables, current version)
- Extension:WikiDB (provides database features, somewhat similar to semantic properties)
- Extension:Infobox Data Capture (Captures key-value pairs, simpler but less functional)