Geronimo support two web containers: Jetty and Apache Tomcat. While Jetty is not an apache project, it was initially selected for Geronimo as it is simpler to embed and Jetty developers are involved with the Geronimo project. As some users have specific requirements for Tomcat, an integration of Tomcat is also available. The ability to switch servlet containers is a demonstration of the flexibility of the Geronimo architecture.
For users that stay within the J2EE specification, it is not important which web container is selected and the default will be suitable. For users with specific requirements or preferences for Jetty or Tomcat, Geronimo supports that choice.