Excerpt from an interview with Salesforce.com chief scientist, JP Rangaswami
TR: What does Chatter do differently from the countless other collaboration tools that have existed?
Rangaswami: The challenge was not in designing a system to collaborate, because as you said, there are millions of them. The challenge was how to take a collaboration mechanism and associate it with systems of record. Systems of record are the replacements for books and ledgers of the firm, and have to be built with a very high degree of security. But the systems of engagement, the ways that people communicate with each other, had to be built on diametrically opposed security principles. And you don't really want all your customer data being e-mailed around. You wouldn't want a list of all your best customers being extracted from your system of record and then mailed by somebody who's leaving the company.
Chatter works securely with Salesforce systems of record—and it can be made to work securely with others, such as software from SAP or Siebel. And it is based around data rather than around messaging.