Difference between force.com site and site.com?

Resolution Force.com Sites:

• Force.com sites supports both authenticated and public websites (i.e. the legacy portal products).
• Included in all Enterprise Edition (or above) and Developer orgs.
• Support for custom pages using Visualforce, JavaScript, CSS.
• Main target audience is for users that are developers familiar with the above languages.
• Can access all Force.com objects.
• A full review of the product is available on this page.

Site.com:

• Formerly called "Siteforce".
• Is a provisioned (paid-for) product.
• Site.com is meant for non-technical administrators as there is no coding necessary.
• Drag n drop support for CMS.
• Allows custom coding using HTML, CSS, Javascript.
• Includes a security model of who can contribute to and publish sites.
• Chatter supported for contribution of content while chatter is not available on the front end website.
• A full review of the product is available on this page.

For the end user, there may be no noticeable difference between a site created via Force.com Sites or in Site.com.

For developers and content managers, the two are very different:

• Site.com is a CMS (Content Management System) that allows developers and non-developers alike to maintain a website. It has WYSIWYG editing and point-and-click page creation and management. Underlying Salesforce functionality is fairly constrained.

• Force.com Sites are websites that are created and coded by developers using Visualforce (an html-like SFDC-view language) and apex code. Nearly every imaginable element of Salesforce functionality is available through code that can be written as part of a Force.com Site.