IBM JZOS Batch Toolkit for z/OS SDKs 

Developed orignally by Dovetailed Technologies, JZOS is now part of the IBM Java SDKs for z/OS

Dovetailed Technologies offers consulting services to assist organizations with integrating JZOS and Java into their z/OS workloads. In addition to the support offered by IBM for JZOS, the Dovetailed Technologies web forum has a JZOS section where users can ask questions and discuss Java on z/OS.

Run Tomcat on Your Mainframe in an Hour or Less!

Using JZOS, running the Apache Tomcat servlet / JSP container is a snap. You can install and configure Tomcat on your mainframe in under an hour.

The web forum has a "Tomcat" section where users can discuss using Apache Tomcat under z/OS.

Open Source Java on z/OS

Apache Tomcat is not the only great open source Java application that runs on z/OS. See the jzos documentation for how to integrate JZOS with DB2, Derby (Cloudscape) and more. The web forumhas a "Open Source" section where users can discuss using various Java open source projects on z/OS.