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 starting with Mac OS X 10.2 Jaguar in August 2002.