Jenova is a Java Web Flow framework built on many open source frameworks and libraries : Struts, JSF, Hibernate, Drools, FOP, JFOR, Axis, Log4J... It provides a declarative way for programming J2EE applications.
Populo is a tool for executing UML models, whose precise behavior is specified by means of the UML action language, with the typical functionalities of a debugger, such as breakpoint-based execution.
The xWire framework is a toolkit used to build Java web applications, but is flexible enough for other uses. It is ideal for building AJAX apps and consists of both client and server components, each of which can be used independently of the other.