Sharepoint Alfresco and Liferay

Liferay, Sharepoint and Alfresco are considered as Enterprise Content Management Systems or ECMs which in essence support Document Management, Web Content Management, Workflow, Enterprise Collaboration, Advanced Search and Administration. However Liferay is in contrast more powerful on its Extensibility and Integration points while others are more forcused towards content collaboration. By integrating Liferay with Sharepoint or Alfresco an enterprise can create a mature editorial process management solution with advance visual content presentation capabilities. Liferay from version 6.1 support this idea by introducing the Content Management Interoperability Services or CMIS interface and OAuth and Open Social Portlet.

For example the enterprise product catalogs, Articles, Newsletters and Video etc. content authoring and collaboration can be done through Sharepoint/Alfresco while web presentation is done through Liferay.

Hippo CMS and Nuxeo ECM are the other content management systems which can be integrated with Liferay. Hippo uses JSR-286  Web Services Remort Portlet WSRP feature to integrate with Liferay while Nuxeo uses CMIS and OpenSocial for the integration. The reference section has links for Liferay Blog posts which explains on how to integrate Twitter Gadjet to a users private page using OAuth and Open Social and how to integrate Alfresco in Liferay using CMIS.

References:
Liferay's Enterprise Portal 6.1 Supports CMIS, Integrates Enterprise CMS Document Repositories
Open Source Alternatives To Microsoft SharePoint
Liferay + CMIS: do not expect too much
Content Management Interoperability Services
Liferay CMIS Repository - Wiki
Liferay Sharepoint - User Guide
Integrating Twitter Gadget in Liferay
Integrating Alfresco 3.4 in Liferay 6.1 via CMIS 1.0