Connect REST API Features | Connect REST API Developer Guide

Action Links
An action link is a button on a feed element. Clicking an action link can take a user to a Web page, initiate a file download, or invoke an API call to Salesforce or to an external server. An action link includes a URL and an HTTP method, and can include a request body and header information, such as an OAuth token for authentication. Use action links to integrate Salesforce and third-party services into the feed so that users can take action to drive productivity and accelerate innovation.

Communities
Communities are branded spaces for your employees, customers, and partners to connect. You can customize and create communities to meet your business needs, then transition seamlessly between them.

Feeds and Feed Elements
In API versions 30.0 and earlier, a Chatter feed was a container of feed items. In API version 31.0, the definition of a feed expanded to include new objects that didn’t entirely fit the feed item model. The feed became a container of feed elements. In API version 32.0, feed elements can be either feed items or generic feed elements. Because feeds and feed elements are the core of Chatter, understanding them is crucial to developing applications with Connect REST API.

Salesforce Files
Use Connect REST API to work with Salesforce Files.

Recommendations
Salesforce provides several types of recommendations, and Connect REST API supports Einstein Next Best Action, custom recommendations for communities, and Chatter recommendations.