The Zimbra Social Platform APIs consist of:
These versioned APIs allow developers to customize and innovate on the platform while not having to worry about breaking changes when new versions of the platform are released (see Maintaining Upgrade Safety). The product was redesigned in the Telligent 6.0 release to be built entirely on these APIs.
The REST v2 web services were initially released in Telligent Evolution 5.0 with each release since adding more functionality. Use the REST v2 web services either when working out of process or even inside widgets with AJAX.
The In-Process API is an upgrade-safe .NET library for building on the Zimbra Social platform. The In-Process API is used when working inside the website (or jobs service).
The Core Widget Extensions (or Widget API) expose the In-Process API classes as plugins that can be used inside Studio Widgets and email templates. The Widget API also includes functionality not provided by the In-Process API that is useful for widgets like pagers, editors, and utilities for parsing dates, making lists from arrays, etc.
Documentation for the default set of widget APIs is available in this wiki: Widget API documentation. Documentation for currently-installed widget extensions can be found on your Zimbra Social site in the Widget Studio in the control panel. Just click on the "API Documentation" link.
Documentation for email templates can be found on your Zimbra Social site in the email settings in the control panel. Just click on the "API Documentation" link.