The Apache Project has released Geronimo 1.1, an open source J2EE application server. Version 1.1 "includes numerous bug fixes as well as improvments to perforance, usability and brand new Plug-in feature that allows a user to dynamically build a server to suit their needs. Also included is a Little-G distribution that provides a subset of Geronimo components in a light weight download form." It's published under the Apache 2.0 license, natch.