Geronimo is a free, open source J2EE™ application server. It comes with everything you need to run standard J2EE applications developed against the J2EE 1.4 specifications, and it is also backward-compatible to J2EE 1.3 and J2EE 1.2. Furthermore, its modular design makes it easy to customize, extend, or replace core server features. And thanks to the open source license, you can download the source code for troubleshooting, to help develop enhancements, or just as a matter of record.

At heart, the Geronimo architecture consists of a small core, and many services loaded on top of that core. Application components and resources are in turn loaded into the services. There are several advantages to this layered approach:

• It is possible to configure a very compact server, running only the services, resources, and applications that are strictly necessary.

• It is easy to add new custom services to the server environment, which can be configured, managed, and accessed by applications just like the default services.

• It's possible to replace the default implementation of any service with an alternative, so long as it implements the same interfaces.

Since the Geronimo 1.1 release, Geronimo includes the Geronimo Plugin system used to build and distribute Geronimo applications and services. Plugins can be installed at runtime and handle dependencies and prerequisites automatically, to make it as easy as possible to install and use new features. Currently available plugins integrate Geronimo with other open source projects, and offer new capabilities to J2EE applications running in Geronimo.