joeq is a Java 2 (JDK 1.3 and 1.4) compatible virtual machine. It is unique in that it is entirely implemented in Java, leading to greater reliability, portability, maintainability, and efficiency. It is also language-independent, so code from any supported language can be seamlessly compiled, linked, and executed dynamically.
MaVerick is a MultiValue database management system. MultiValue databases are said to be one of the computer industry's best kept secrets. First appearing over 30 years ago as PICK, they have continued to evolve through various commercial vendors, and are still in active development today. They are very resource friendly, are incredibly fast, feature a very user friendly data retrieval and reporting language (variously called ACCESS or English), and a rapid application development language based originally on Dartmouth Basic. The MaVerick project is an attempt to create an open source variant, written in Java.
Janino is a compiler that reads a Java expression, block, or source file, and generates Java bytecode that is loaded and executed directly. It is not intended to be a development tool, but an embedded compiler for run-time compilation purposes, such as expression evaluators or "server pages" engines like JSP.
The Runabout is an extension of the Java libraries that adds two-argument multi-dispatch to Java without changing the language or the VM. It uses reflection to find visit methods, which are invoked using dynamically generated and loaded code. The Runabout does not need a special compiler or changes to Java's syntax. Dispatch with the Runabout is fairly fast, typically a factor of two to ten times slower than double dispatch. The Runabout is useful since it can help to make code faster and more readable. For example, a sequence of instanceof tests is a clear sign that a Runabout should be used instead.
Just4Log is a library to dynamically enhance the performance of various Java logging systems inside a Java application. The source code in Java is not modified, but the optimization occurs on the compiled bytecode files. It optimizes bytecode from Log4j, Apache Commons, and JDK 1.4 java.util.logging. It can also automatically add "enter" and "exit" logs at every exit and entry point of methods. An Ant task offers integration in Ant scripts.
SuperWaba is a VM for PDAs. Because of the way it was written, you can use Java to develop programs for it. It supports exceptions, threads, many user interface controls, double and long 64-bit types, grayscale, color, 3D controls, and JNI and Java libraries, among other features. The project has been superseded and replaced with TotalCross.
FrAid (Fr[actal] Aid) is a programming language that is appropriate for mathematical computations, visualization, batch processing, and more. It features both a standalone application that provides a programming environment for the language and a system for integrating the language with Java. The Java interface allows mathematical equations and formulas to be used with Java code, making it easier to process numerical computations, symbolic computations, imaging, CAD, and more.