Liferay is an open source JSR 286 compliant portal and social platform, written in Java. It provides fully functional built-in portlets (60+) and also various integration points to seamlessly integrate with other third-party softwares like Alfresco, Sharepoint etc.
Liferay is an open source Java portal that supports portlets and themes. It can be heavily customized and extended with "hook", and "ext" plugins.
As a server it may run on a wide variety of application servers and databases.
It also integrates with a large number of external services and protocols such as CAS, LDAP, and the OpenSocial standard.