WSO2 Application Server can run as a standalone server out of the box. Also, it can be integrated with Apache Tomcat, Apache Geronimo, JBoss, WebLogic, IBM WebSphere application servers etc.
Deploying the WSO2 Application Server correctly on your infrastructure is a vital task for the success of its usage. You should first analyze the requirement and then select the best matching deployment mode. There are different sets of possible deployment modes with different configurations. Some common ones are discussed here.