MUG is a component-based Java Web Framework. Lightweighted and conceived to be easy to use yet flexible, it provides the developer a set of components that allows object-oriented development in a web (in the line of SWT / Swing).
Bimbo is a Java web framework to construct web applications using only annotated POJO's. The idea behind it is that a developer should not bother about look and feel of an application, but to let the framework handle all these details.
Spider is a Java framework for creating web applications. Its major design goals are are testing, reducing boilerplate code, avoiding static state through dependency injection, strict M-V-C separation and convention over configuration.
Marko is a lightweight, action-based web framework for Java with support for multiple templating engines (Freemarker, Velocity, etc). Configuration is done in code (no XML).
(F)irm, (F)ast, (F)lexible and (F)ree Java Web Framework. Supports RESTful web services in a manner roughly based on JAX-RS and Jersey. Prevents mixing presentation and business layer by powerful template system and flexible, reusable components.