Hi John,
now I see what your question was
You can use entity beans without an application server because the Java persistence API with its entity manager and other parts also works for standalone application. If I remember correct the JPA specification and development was split from the EJB technology for these reasons and to be developed further separately.
But some things like dependency injection of an entity manager or transaction handling don't work the same way as in an application server. And not to forget: You MUST use an entity manager which would be part of your application server in an enterprise application. So you really don't use ONLY the entity POJOs but you need the JPA and entity manager.
It's nearly the same with session beans. Of course you can use them in standalone application because they are simple POJOs. But you need something like a framework or an application server to benefit from the functionality an application server would give your session beans.
Unfortunately I don't know of something smaller or less heavy-weight framework which uses the same annotations and provides you similar functionality like an application server. Perhaps
you should use a totally different technology? The Spring framework or some dependency injection containers for example could provide some parts of the functionality of an application server. To get good advices for some framework you probably first should know what you'd really expect from a runtime environment for your kind of "session beans". Security management? Transaction handling? Dependency injection? Lifecycle management?
Despite this I'd like to know what problems do you have with application servers? As James pointed out current application servers like Glassfish,
JBoss etc. are really mature and easy to run and not too much heavy-weight. If you want to support really many users you should of course use a powerful machine. But at least applications servers are very scalable and a standalone application would perhaps suffer from this problem. And for normal usage an ordinary desktop computer or small server will be absolutely sufficient.
So think about what you really want to achieve! Unfortunately I don't know of a good framework to use as an alternative without an application server. But perhaps someone other?!?
Marco