A typical enterprise uses many applications, many or most of which are not designed to work with one another out of the box. Integrating separate but related apps helps organizations achieve greater levels of operational consistency, efficiency, and quality.
Each application can have data, business logic, presentation, and security layers, all of which are possible targets for integration.
With force.com you can integrate your local application and web application as well.
• Salesforce to Google App
• Salesforce to Microsoft dynamic
• Salesforce to Quick-book
• Salesforce integration with Magento
• Salesforce integration with amazon
• Salesforce integration with sap