Description: Ehcache is a widely used java distributed cache for general purpose caching, Java EE and light-weight containers.
Main Site: http://ehcache.sourceforge.net/
See Also: EHCache Integration Guide

Description: Hibernate is a powerful, high performance object/relational persistence and query service. Hibernate lets you develop persistent classes following object-oriented idiom - including association, inheritance, polymorphism, composition, and collections. Hibernate allows you to express queries in its own portable SQL extension (HQL), as well as in native SQL, or with an object-oriented Criteria and Example API.
Main Site: http://www.hibernate.org/
See Also: Hibernate Integration Guide

Description: The iBATIS Data Mapper framework makes it easier to use a database with Java and .NET applications. iBATIS couples objects with stored procedures or SQL statements using a XML descriptor. Simplicity is the biggest advantage of the iBATIS Data Mapper over object relational mapping tools.
Main Site: http://ibatis.apache.org/

Description: RIFE is a full-stack web application framework with tools and APIs to implement most common web features.
Main Site: http://rifers.org

*Description:*Spring Framework is the leading full-stack Java/JEE application framework.
Main Site: http://www.springframework.org/

Description: Apache Struts is a free open-source framework for creating Java web applications.
Main Site: http://struts.apache.org/

Description: Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java. It is a technology suitable for nearly any application that requires full-text search, especially cross-platform.
Main Site: http://lucene.apache.org/java/docs/

Description: Quartz is a full-featured, open source job scheduling system that can be integrated with, or used along side virtually any J2EE or J2SE application - from the smallest stand-alone application to the largest e-commerce system.
Main Site: http://www.opensymphony.com/quartz/

Description: With proper mark-up/logic separation, a POJO data model, and a refreshing lack of XML, Apache Wicket makes developing web-apps simple and enjoyable again. Swap the boilerplate, complex debugging and brittle code for powerful, reusable components written with plain Java and HTML.
Main Site: http://wicket.apache.org/

Description: CAS provides enterprise single sign on service
Main Site: http://www.ja-sig.org/products/cas/

Description: Compass is an open source project built on top of Lucene aiming at simplifying the integration of search into any Java application.
Main Site: http://www.compass-project.org/

Description: iPoint portal is an open source, standards compliant portal server, which combines Content Management capabilities with groupware collaboration to enable users to create customisable Internet, Extranet and Intranet sites directly through their browser with no technical expertise.
Main Site: http://www.c2b2.co.uk/iPoint/1.page

Description: Liferay Portal is the world's leading open source enterprise portal solution using the latest in Java and Web 2.0 technologies.
Main Site: http://www.liferay.com/web/guest/home

ODAL

Description:
Objective database abstraction layer (ODAL) is a high-performance multi-purpose (see below) database manipulation framework. Features include query API, O-R mapping, data validation/conversion, stored procedure support, code generation.
Main Site: http://odal.sourceforge.net/odal-guide.xhtml#1.9.18.1.Terracotta%20Cache%20Clustering

Description: Repast Simphony is a free and open source agent-based modeling toolkit that simplifies model creation and use.
Main Site: http://repast.sourceforge.net/

Rhino in Spring

Description: Rhino in Spring is a project that intends to integrate Mozilla Rhino JavaScript interpreter, the interpreter for the best (in our opinion) dynamic language on the Java platform with Spring Framework, the also best (again, in our opinion) enterprise framework on the Java platform. The aim is to provide a system that amalgamates the rapid development benefits and flexibility of a dynamic language with the strength, scalability and versatility of the Java platform and the Spring framework.
Main Site: http://rhinoinspring.sourceforge.net/

Description: Sakai is an online Collaboration and Learning Environment. Many users of Sakai deploy it to support teaching and learning, ad hoc group collaboration, support for portfolios and research collaboration.
Main Site: http://sakaiproject.org/

Description: Scarlet is a clustering extension for Atlassian Jira.
Main Site: http://scarlet.sourceforge.net/

Description: SemiSpace is an interpretation of Tuple Space / Object Space based on ideas from JavaSpaces . It can be run as single, stand alone, space on one J2SE 5.0 VM (or greater), or clustered with Terracotta.
Main Site: http://www.dynamicus.org/semispace/

Description: SmartFoxServer is a comprehensive and powerful platform
for rapidly developing multiuser applications and games with Macromedia Flash MX, MX 2004, 8, Flex 2 and Flash CS3.
Main Site: http://www.smartfoxserver.com/

Description: Camel implements the Enterprise Integration Patterns allowing you to configure routing and mediation rules in either a Java based Domain Specific Language (or Fluent API) or via Spring based Xml Configuration files. Either approaches mean you get smart completion of routing rules in your IDE whether in your Java or XML editor.
Main Site: http://activemq.apache.org/camel/

Description: Groovy is an agile and dynamic language for the Java Virtual Machine
Main Site: http://groovy.codehaus.org/

Google Guice

Description: Guice alleviates the need for factories and the use of new in your Java code. Think of Guice's @Inject as the new new. You will still need to write factories in some cases, but your code will not depend directly on them. Your code will be easier to change, unit test and reuse in other contexts.
Main Site: http://code.google.com/p/google-guice/

Description: JCS is a distributed caching system written in java. It is intended to speed up applications by providing a means to manage cached data of various dynamic natures. Like any caching system, JCS is most useful for high read, low put applications. Latency times drop sharply and bottlenecks move away from the database in an effectively cached system.
Main Site: http://jakarta.apache.org/jcs/

Joda-Time

Description: Joda-Time provides a quality replacement for the Java date and time classes.
Main Site: http://joda-time.sourceforge.net/

Description: Scala is a general purpose programming language designed to express common programming patterns in a concise, elegant, and type-safe way. It smoothly integrates features of object-oriented and functional languages. It is also fully interoperable with Java.
Main Site: http://www.scala-lang.org/