REST API includes new, changed, and deprecated calls in addition to new invocable actions.
Chatter REST API
Integrate mobile apps, intranet sites, and third-party web applications with Salesforce using Chatter REST API. Include hyperlinks in posts, purge mission activity for users, and take advantage of generally available Next Best Actions.
Reports and Dashboards REST API
The Reports and Dashboards REST API has been enhanced to support the beta release of historical tracking report enhancements in Lightning Experience.To support this feature, the /analytics/report-types/ resource has a new property and the /analytics/report-types/type resource supports a new report type.
User Interface API
Build Salesforce UI using the same API that Salesforce uses to build Lightning Experience and Salesforce for Android, iOS, and mobile web. Build user interfaces that let users work with records, list views, actions, favorites, and more.
Tooling API includes new and changed objects.
Metadata API includes new and changed types and fields.