The Apache Open For Business Project is an enterprise automation software project that includes ERP, CRM, E-Business/E-Commerce, SCM, MRP, and CMMS/EAM functions. It is a foundation and starting point for enterprise solutions and can certainly be used out of the box, but is also great for creating specialized applications.
Spring is a lightweight Java/J2EE application framework based on code published in "Expert One-on-One J2EE Design and Development" by Rod Johnson. It includes powerful JavaBeans-based configuration management applying Inversion-of-Control principles, a generic abstraction layer for transaction management allowing for pluggable transaction managers, a JDBC abstraction layer, integration with Hibernate, JDO, Apache OJB, and iBATIS SQL Maps, AOP functionality, and a flexible MVC Web application framework with multiple view technologies. There is also a .NET port available.
Compass is a Java framework which makes it simple to map your Java object model into a search engine. It is built on top of the Lucene search engine. Compass features declarative mapping technology OSEM (similar to O/R database mapping), transaction management, Google-like query syntax, externalization of common metadata, and much much more.
Chessweb is a J2EE chess game Website. It is a pure Java servlet implementation of a two-player chess game. Two players log into the Web site, see an image of the current board in their browser, and make their moves. The differentiating features of chessweb (e.g. versus WinBoard / XBoard) is that it's an extremely lightweight implementation written completely in Java (nothing more than an app server and browser is required). Furthermore, the client end is DHTML only, and verified to works with FireFox 1.0.6 and IE 6.
The ZK Mobile is a ZK extension that enables ZK applications to run on mobile devices with little programming. With the event-driven components and a markup language, programming is as simple as programming desktops and designing screens is as easy as authoring HTML pages. No JavaME prerequisite is required.