finally selling, but by this point, the market was moving toward SMTP-based Internet mail as a universal format. By 1996 Apple had given up on AOCE, and started talking about the CyberDog project based on the OpenDoc platform. AOCE is not supported in Mac OS 7.6. Overview AOCE's Open Directory and related software introduced the concept of directory entries (such as business cards) as first-class desktop objects. This is used to create a drag-and-drop metaphor for mail, fax, and other directory-based activities. Each endpoint, a mail server for instance, is driven by a plug-in extension that is driven by a common AOCE-supplied queue and queue viewer. PowerTalk provides a set of standard forms for interacting with the items in the queues, and a common interface for mail, and a universal mailbox. Encryption is supported by a single keychain that remembered all your passwords and digital signatures, encrypting them together so only a single password needed to be remembered. The system was designed in an era when there were many email formats and services, including online services such as CompuServe and AppleLink, networking standards like X.400 and SMTP (Internet mail), and LAN-based servers such as Microsoft Mail and QuickMail. In order to support this diverse environment, AOCE includes a robust layered protocol stack that, in theory, can be used with practically any store-and-forward type of environment. This is used within AOCE not only to service mail, but faxes, printing and even directly sending files from one machine to another without enclosing them in a mail message or needing a file server. Adoption of AOCE among third party developers was slow due to a complicated API. The book documenting the system is larger than all of the books describing the rest of the pre-System 7 Macintosh combined. Adding a simple feature like "mail this document" to an application requires wading through hundreds of pages of documentation, and writing a core AOCE component is many times more complex. Several parts of the AOCE engine are useful on their own, such as the Keychain. However, in order to get the keychain, the user must install all of AOCE, a cost the users were not willing to pay. Many years later the keychain was finally shipped as a stand-alone component in Mac OS 9. The encryption and signing support is arguably also useful (although not widely deployed), and it reappeared in Apple's bundled Mail application