Pluto, Jetspeed 2, EXO Portal, Liferay, ...
Sean Goggins gave a very thorough presentation on the Java Portlet Specification (JSR 168) and demoed with multiple implementations.
Things I learned:
- Pluto is a reference implementation of a JSR 168 compliant portlet container (not to be confused with a portal). It's an Apache project (originated from IBM?)
- Jetspeed 2 is a servlet based implementation of a portal that uses Pluto as its portlet container. It's also an Apache project.
- EXO Portal is another servlet based implementation of a portal that supports JSR 168 conforming portlets.
- Liferay is a J2EE based implementation of a portal that can be deployed in any J2EE app server.
- WebSphere, BEA, SAP, Novell, Oracle all have their own implementations of portals.
- You write portlets much like you write servlets. And you can deploy them in any compliant portlet containers.
The presentation material is here.