Force.com Sites technology is used to build public facing websites that run on the Force.com platform. The pages of a Force.com Site are built with Visualforce. Force.com Sites is one of the two Salesforce technologies, Site.com being the other, for constructing public facing websites.
Questions related to the administration, design, development, usage, or any other part of Force.com Sites are appropriate for this tag.
Force.com Sites and Site.com are the two Salesforce technologies that can be used to publish public facing websites. Force.com Sites can use Visualforce and Apex directly whereas Site.com cannot. Force.com Sites is not a Content Management System (CMS) like Site.com; however, there are CMS AppExchange Apps that can be used in conjunction with Force.com Sites to provide a CMS experience without Site.com.
Force.com Sites together with Customer Portal can be used to provide authenticated Force.com Sites; however, at this time custom SSL certificates are not supported so all https requests use the secure.force.com domain.
The developerforce page for sites is a central page that contains links to suggested learning paths, sites resources, demos, webinars, and a gallery of live sites.
An Introduction to Force.com Sites provides a thorough introduction to Force.com Sites.
Salesforce's Force.com Sites Implementation Guide is the main reference for Force.com Sites.