OpenEJB is an open-source, embeddable and lightweight Enterprise JavaBeans Container System and EJB Server, released under the Apache License 2.0.
Rather than join the space as a competitor, the project was focused entirely on providing these new platforms with a way to quickly get EJB compliance via plugging OpenEJB into their application server.
The test suite was developed as a generic application since it would need to be run against both WebObjects and other platforms that integrated OpenEJB.
For simplicity in the build the test suite based on JUnit, was run with OpenEJB right inside the tests rather than as a separate process, which was easy to do as the container was designed to be plugged into other platforms and make as little assumptions about its environment as possible.
In 2006 when EJB 3.0 was released which had a focus on simplicity, the project went back to its roots and revived the OpenEJB 1.0 codebase, ported select bits of the 2.0 codebase, and eventually brought it up to the EJB 3.0 spec level in what is now called OpenEJB 3.0.