The developer APIs for release 8.5 are located here: http://community.zimbra.com/developers/w/developer85
Provide a read-only list of enabled rules per site. Additionally the Rules engine allows you to add custom actions and triggers for your own needs using the plugin model.
Using the plugin model you can create additional content conversion implementations that allow you to convert content from one type to another in additional to the existing Status message to forum thread converter available.
The new LDAP login plugin is extensible through the public API.
The Cookie Authentication SSO module is now extensible using a new public API.
Forms authentication is supported in the API.
Windows Authentication has been ported to the public API.
APIs have been added to support versioned installation of content fragments for third party applications that want to allow sites to maintain versioned widgets during upgrades.