Out of a bit of an experimental exercise evolved the Little Portal Gizmo, a small web application container. The idea was to directly use Eclipse's plug-in infrastructure to support the development of web applications.
The Gizmo uses the Apache HTTP Core as its HTTP protocol engine. Instead of implementing the Java Servlet API, it uses a custom and very light weight API that in many aspects derives directly from the underlying Apache HTTP Core library.
The web applications you develop for the Gizmo have the form of Eclipse plug-ins. So if you know your way around plug-in development and are familiar with e.g. extension points, plug-in manifests and the lot, you know you're at home.
The Gizmo is young and wild, still needs a fair bit of taming and grooming. It might be a fun ride, though!
Here's where it lives: http://lipog.sourceforge.net