In existence since the beginning of time and which will continue being used long after the hype has waned.
- Apache Ant - Build process management with XML.
- Apache Hadoop - Storage and large-scale processing of data-sets on clusters of commodity hardware.
- Apache OpenNLP - Toolkit for common tasks like tokenization.
- Apache Velocity - Templates for HTML pages, emails or source code generation in general.
- FreeMarker - General templating engine without any heavyweight or opinionated dependencies.
- GlassFish - Application server and reference implementation for Java EE sponsored by Oracle.
- GWT - Toolbox which includes a Java-to-JavaScript compiler for client-side code, XML parser, API for RPC, JUnit integration, internationalization support and widgets for the GUI.
- HornetQ - Clear, concise, modular and made to be embedded.
- Hudson - Continuous integration server still in active development.
- Java Modeling Language (JML) - Behavioral interface specification language that can be used to specify the behavior of code modules. It combines the design by contract approach of Eiffel and the model-based specification approach of the Larch family of interface specification languages, with some elements of the refinement calculus. Used by several other verification tools.
- JavaCC - More specific and slightly easier to learn. Has syntactic lookahead.
- JavaServer Faces - Oracle's open-source implementation of the JSF standard, Mojarra.
- JavaServer Pages - Common templating for websites with custom tag libraries.
- JUnit - Common testing framework.
- Launch4j - Wraps JARs in lightweight and native Windows executables.
- Quartz - Open-source job scheduler library with Apache 2.0 license.
- TestNG - Testing framework.
- Trove - Primitive collections.