Remember back in the days (or was it hours) of the Internet bubble how hot the whole idea of portals was? I always like the concept as it captured the granular nature of a set of user-configurable productivity services. Well, it seems that after lying fallow for the few years after the term fell out of favor it is now making a huge reappearance. And to prove this assertion just try a search on Google for "open source portal" - I got 87,300,000 hits!Today I'm going to discuss a very popular portal system called Liferay Portal. Liferay is a Java application that will run on any Java 2 Enterprise Edition Platform (J2EE) server which also means, of course, that it will also run on any operating system.Liferay Portal, current Release 3.6.1, is also free and open source (under the MIT License) with a huge list of features. Out-of-the-box Liferay provides many different portlets (the individual service elements represented by individual windows) including blog, calendar, document library, journal (CMS), image gallery, mail, message board, poll, newsfeed, navigation (entire site structure layout), breadcrumb (simple navigation to the current page) and wiki.Supporting the included portlets is a huge range of features that includes:* Custom layouts with the ability to position portlets in a layout using drag and drop.* Support for multiple instances of the same portlet.* Content management system functionality via a set of portlets.* Support for JavaServer Faces-based portlets.* "Hot deploy" themes (the ability to change presentation themes without a server restart).Liferay also offers support for a variety of single sign-on services, multiple Liferay instances (required to support applications service environments), clustering, internationalization and personalization.Liferay is application server agnostic and will work under Borland ES, JBoss+Jetty\/Tomcat, JOnAS+Jetty\/Tomcat, JRun, OracleAS, Orion, Pramati, RexIP, Sun JSAS, WebLogic, and WebSphere. Liferay is also database agnostic (it has been tested with DB2, Firebird,Hypersonic, InterBase, JDataStore, MySQL, Oracle, PostgreSQL, SAP, and SQL Server) and uses Hibernate for persistence. In fact, Liferay runs on such a wide variety of servers and subsystems that there is a huge deployment matrix to help you select the right combinations.Particularly interesting is Liferay's support for Web Services for Remote Portlets (WSRP), a specification from Organization for the Advancement of Structured Information Standards (OASIS). According to OASIS, WSRP is "a Web services standard that allows you to publish portlets from your portal to external portals and allows you to consume portlets in your portal from external portals."Liferay has some impressive success stories. The latest is having been selected as the platform for Walden Media's "Chronicles of Narnia" educational site, in which it must be very successful as the site's performance is, at the time of writing, atrocious!I do know however, that Liferay's performance is actually very good and as the basis for an intranet or customer portal system it has to be one of the most flexible and sophisticated choices available.