Video: Documentum vs SharePoint

Documentum provides management capabilities for all types of content including business documents, photos, video, medical images, e-mail, Web pages, fixed content, XML-tagged documents, etc. The core of Documentum is a repository in which the content is stored securely under compliance rules. This repository appears as a unified environment, although content may reside on multiple servers and physical storage devices within a distributed environment. Free open-source Documentum alternatives - Alfresco, Nuxeo, Liferay Portal.
SharePoint's multi-purpose platform allows for managing and provisioning of intranet portals, extranets and websites, document management and file management, collaboration spaces, social networking tools, enterprise search, business intelligence tooling, process/information integration, and third-party developed solutions. SharePoint can also be used as a web application development platform. SharePoint alternatives for small business are: Office 365, Box, G Suite, Zoho. There are also free open-source alternatives to Sharepoint - Alfresco, Nuxeo, Liferay Portal.
Face to face in the news:

2003 - EMC acquired Documentum for $1,7 billion to win over SharePoint

The data storage giant EMC has acquired the web-platform for enterprise content management Documentum for $ 1.7 billion. The Documentum acquisition is intended to strengthen the EMC market share in its competition with IBM. Now the users of EMC storage systems will be able to get their hands on more efficient content management tools. Cooperation between EMC and Documentum began last year when the companies developed the storage and digital archive management solution for EMC Centera. Now, this cooperation will continue in a new form - Documentum will become a division of EMC.