Today, 75% of Twitter traffic and 65% of Salesforce.com traffic comes through APIs. But APIs are not just for the social Web. According to ProgrammableWeb.com, the number of open APIs being offered publicly over the Internet now exceeds 2000—up from just 32 in 2005. Opening APIs up to outside developers enables many technology start-ups to become platforms, by fostering developer communities tied to their core data or application resources. This translates into new reach (think Twitter’s rapid growth), revenue (think Salesforce.com’s AppExchange) or end user retention (think Facebook).