Force.com is a cloud computing platform as a service from
Salesforce.com, that developers use to build multi tenant
applications hosted on their servers as a service. The platform
allows external developers to create add-on applications that
integrate into the main salesforce.com application and are hosted
on salesforce.com's infrastructure. These applications are built
using Apex (a proprietary Java-like programming language for the
Force.com platform) and Visualforce (an XML-like syntax for
building user interfaces in HTML, Ajax or Flex).