So what is S2AP?
The S2AP is the Spring Dynamic Modules Kernel, running on top of Equinox, hosting a Tomcat server, with a specialized management interface, with some funky new advantages. So you get a Java EE application server with OSGi dynamic modules and all the power of the Spring Framework. Awesome!
The platform aims at being a lightweight, customizable Java EE Server, with a preference for Spring-oriented applications. The platform has no trouble running applications that were not built with Spring technologies though, it accepts standard Java EE WAR-files and also standard OSGi bundles.