Below a comparaison of available SharePoint 2019 webparts and Office 365

WebParts available in SharePoint 2019 Preview

Missing WebParts compared to Office 365 (As of 02 08 2018 in SharePoint 2019 Preview)

1. Category Text, media, and content
   
   1. Kindle instant preview
2. Category Discovery
   
   1. Sites
3. Category Communication and collaboration
   
   1. Group Calendar
   2. Microsoft Forms
   3. Twitter
4. Category Planning and process
   
   1. Planner
5. Category Business and intelligence
   
   1. PowerBI
6. Connectors (Asana, bitbuckets, facebook, github, github enterprise, google analytics, incoming webhook)
7. Category Others :
   
   1. Banner, followed Sites, links, lob integration, page properties, people directory, personal calendar, personal