OpenEJB is a simple, lightweight Enterprise JavaBeans (EJB) container and server. You can embed OpenEJB in your own applications, or in a Web application server like Tomcat, or run it as a standalone EJB server. It supports EJB 3.0, 2.1, 2.0, and 1.1, and has partial support for EJB 3.1.
EJOE is a lightweight Java remoting framework built to send and receive objects through pluggable (de)serialization mechanisms. It offers a high-performance, simple, and clean object request broker (whereby ORB is meant in its natural manner and not in its relation with CORBA), with server and client components for your client/server applications. It's a highly scalable implementation of the common request-process-response pattern based on Java NIO. It does support optional remote class loading to avoid redundant classpath entries, but doesn't require stubs and/or proxy objects.
Apache ActiveMQ is a popular and powerful message broker and enterprise integration patterns provider. Apache ActiveMQ is fast, supports many cross language clients and protocols, comes with easy-to-use enterprise integration patterns and many advanced features, while fully supporting JMS 1.1 and J2EE 1.4.