You can run it as a standalone application. Keep all the JBPM5, Drools and the dependant jar files in CLASSPATH and you can run it as a normal Java application.
If you have human tasks that require approvals, you need a webserer. It can be JBoss, Tomcat, Weblogic,Websphere or even .Net.
As long as you create a service using JBPM5, you can invoke it from another standalone or web application.