Historically, online media tend to start this way. The early services, such as CompuServe, Prodigy or AOL, began as “walled gardens” before they opened up to become websites. The early e-mail services could send messages only within their own walls (rather as Facebook's messaging does today). Instant-messaging, too, started closed, but is gradually opening up. In social networking, this evolution is just beginning. Parts of the industry are collaborating in a “data portability workgroup” to let people move their friend lists and other information around the web. Others are pushing OpenID, a plan to create a single, federated sign-on system that people can use across many sites.