Groovy is an agile, dynamic language for the JVM which combines many features from languages like Python, Ruby, and Smalltalk and makes them available to Java developers using a Java-like syntax. It is designed to help get things done on the Java platform in a quicker, more concise, and fun way. It can be used as an alternative compiler to javac to generate standard Java bytecode to be used by any Java project or it can be used dynamically as an alternative language, such as for scripting Java objects, templating, or writing unit test cases.
Squirrel is a light-weight programming language (around 6000 lines of code) that features higher-order functions, classes/inheritance, delegation, tail recursion, generators, cooperative threads, exception handling, reference counting and garbage collection on demand. It has a C-like syntax.
Jess is a fast, light rule engine and scripting environment written entirely in Java. You can build Java software that has the capacity to "reason" using knowledge you supply in the form of declarative rules. It is supplied as a programmer's library, making it ideal for embedding in larger applications. Jess includes development tools built on the Eclipse platform. It is free for academic use and can be licensed for commercial use.
Java Development Environment for Emacs (JDEE) is an Emacs-based integrated development environment (IDE) for developing Java applications and applets. Features include multiple code browsers, a JPDA-based debugger, method and field completion, template-based and procedure-based code generation, Java source code interpreter, context-sensitive help, and more.
ActivePython is the industry-standard Python distribution, available for Windows, Linux, Mac OS X, Solaris, AIX, and HP-UX. It is 100% compatible with the reference distribution of Python. Code tested with ActivePython will run on any Python installation that has the appropriate extensions installed.
Gauche is an R5RS Scheme implementation that aims to be a handy tool for daily work. Quick startup, a built-in system interface, and native multilingual support are some of its goals. It has an OO system similar to STklos and Guile. It supports UTF-8, EUC-JP, and Shift-JIS multibyte encodings natively.
MDK (MIX Development Kit) provides tools for developing and executing, in a MIX virtual machine, MIXAL programs. The MIX is Donald Knuth's mythical computer, described in the first volume of The Art of Computer Programming, which is programmed using MIXAL, the MIX assembly language. MDK includes a MIXAL assembler (mixasm), a MIX virtual machine (mixvm) with a command line interface, a Guile-based virtual machine (mixguile), a GTK+ based GUI (gmixvm), and a mixvm-Emacs interface (mixvm.el). MDK utilities are extensible using Scheme.