An open source framework for building Servlet/JSP based web applications based on the Model-View-Controller (MVC) design paradigm [Open Source, BSD-like]

Cocoon is an XML based servlet framework.

Official Documentation and Reference Implementation

Offers servlet software, mailing lists, servlet-capable ISP list, engines, tools, articles, and examples, from Jason Hunter, author of "Java Servlet Programming" (O'Reilly).

Cactus is a testing framework that allows you to create unit tests for your servlets.

Java-Servlet web host supporting v2.3 and v2.4 servlet specification.

Resource center for servlet development, including articles and free servlet downloads.

Collection of servlets to handle file uploads, send email, cache responses, generate server push pages, parse parameters, and negotiate locales for internationalization.

Access to Java Servlet 2.3 and JavaServer Pages 1.2 specifications.

Enhydra XMLC is a presentation engine that enforces a strict separation of markup and logic.