Anybody can implement the java ee specification (JSR342), or any jsr that's part of it. When they do, they can (after buying and passing Compatibility Test Suite) claim to be compatible with the specification. There is a number of vendors with their application servers which are compatible with java ee, but no vendor implement full java ee specification. For instance, glassfish (the java ee reference implementation) uses Red Hat's CDI implementation. Sometimes, the vendor does not implement any part of the java ee specification, they grab glassfish, add their vendor specific libraries, and release it under their name. To claim compatibility, they still need to go through the certification process and run CTS.
To find out all the vendors who implement the specification is not so easy, since not all of them go through the certification process. For instance, Apache CXF is not certified on its own, rather it gets certified as part of Red Hat's JBoss.
Each specification has an API and a written pdf, both of which define the mandatory behaviour of each implementation. That is what you use when write EJB code. For instance, when you create an ejb:
import javax.ejb.Singleton;
@Singleton
public class MySingleton{
...
}
@Singleton annotation is part of the specification, but MySingleton class is your EJB code, it's not part of the specification. The EJB container then knows what to do with the class.
