Starting today, developers worldwide can integrate LinkedIn into their business applications and Web sites. Developer.linkedin.com is now live and open for business.

The evolution of the LinkedIn Platform
Over the past months, LinkedIn has supported integrations with some of the most prominent and critical software applications in the enterprise. Partnerships with companies like IBM, Blackberry (Research in Motion), and most recently Microsoft, have given us time to invest in both functionality and scalability of the platform.
Source: http://blog.linkedin.com/2009/11/23/linkedin-platform-launch/