I am looking for a opensource lightweight Application server(J2EE standard compliant) that could be emmbeded in custom applications for standalone use (for single user only). Right now a similar application is running on customised Tomcat4 but still its pretty heavy and has many additional features that we do not use but are not able to detach from it.
Please advise if you know of a more suitable app server for such applications.
If you're using only jsp/servlets you should consider jetty. If you want a more complete solution, look the jetty/jboss combination.
Hope this help,
If the application is non-commercial (or even a smaller startup) and you don't care about open-source as much as paying $0/cpu, then I'd go with Resin over any of those open source initiatives. When you say light-weight, I'm also assuming you really mean performant (since light-weight servers that lack advanced features SHOULD be faster). In practice though, Resin and Orion are better when it comes to raw speed for low cost solutions. With Orion it's free and Resin you pay $25. As you can see, JBoss/Jetty looks like a pretty poor decision from this perspective.
If you really need opensource, the whole light-weight question doesn't matter. JBoss and it's surround technologies is your only real option other than Tomcat. There isn't a lot of choice there.
If you check out the news section on this site you will find an article about ZeoSphere( Just Read it Myself) its a mobile devices EJB Server. Might look into it.