is a CRM system which has built in OOB functionalities to automate your Sales, Marketing, Services etc. We call this as SaaS (Software-as-a Service). is a Platform-as-a-Service (PaaS) offering from the same company that allows you to build your own applications and/or customize the standard applications. also offers which as Platform-as-a-Service (PaaS) framework using which you can:

a) Customize and extend the core functionality offered by Salesforce
b) Create new applications and/or products

In layman language bellow is the difference between the two- = iPhone OS.  The environment that can build and run apps. = The iPhone “app” that stores contacts, makes phone calls, + all the other standard functions of a phone. runs on the platform, much like the iPhone dialer runs on the iPhone OS.

If we dig a little more in details, the difference would go as below-

When you sign up for‘s “sales cloud” – you get the CRM functionality that’s pre-built by Salesforce. You can use other tools) to customize your CRM or build new applications that are housed within your salesforce instance (organization). includes the following major building blocks for building your applications:

a) Apex – Java like programming language for building your application logic(Controller)
b) Visualforce – for building application user interfaces(View)
c) Custom Objects – for storing your data(Model)

Apart from the above, the platform also includes other shared framework components that you can leverage – such as scheduling engine, email service, public facing websites etc etc.

Interestingly anecdotal references state that most of is NOT built using – except for may be some pieces.