SLIME is an integrated development environment for Common LISP which does everything you would expect from an IDE: code evaluation, compilation, macro expansion, and auto-completion. It also finds definitions of functions, and marks LISP forms which the compiler finds to be erroneous. It provides easy access to implementation-specific online documentation as well as the ability to look up symbols in the ANSI Common Lisp HyperSpec. Further, it includes an interactive debugger and object inspector.
Nyquist is an elegant and powerful language for sound synthesis and music composition. Unlike score languages that tend to deal only with events, or signal processing languages that tend to deal only with signals and synthesis, it handles both in a single integrated system. It is also flexible and easy to use because it is based on an interactive Lisp interpreter. You can design instruments by combining functions (much as you would using the orchestra languages of Music V, cmusic, or Csound). You can call upon these instruments and generate a sound just by typing a simple expression. You can combine simple expressions into complex ones to create a whole composition. It runs under any Unix environment, MacOS, Windows 95, and Windows NT, and it produces sound files as output (or direct audio output under Windows).
The Regex Coach is a graphical application for Linux and Windows which can be used to experiment with (Perl-compatible) regular expressions interactively. It shows whether a regular expression matches a particular target string, and can also show which parts of the target string correspond to captured register groups or to arbitrary parts of the regular expression. It can "walk" through the target string one match at a time and simulate Perl's split and s/// (substitution) operators. It tries to describe the regular expression in plain English. It can show a graphical representation of the regular expression's parse tree. It can single-step through the matching process as performed by the regex engine. Everything happens in "real time" (i.e., as soon as you make a change somewhere in the application all other parts are instantly updated).
RScheme is an object-oriented, extended Scheme implementation with a compiler that targets C or (RScheme's own) bytecodes. It has features expected from a modern language: an object system, reflection, modules, namespaces, safe macros, threads, a system call interface (including sockets), separate compilation, and persistence, as well as the formal basis and power of the Scheme programming language. RScheme also features a powerful, elegant foreign code interface.
XSLT-process is a minor mode for (X)Emacs that allows you to run a Java XSLT processor on a buffer and display the result in another buffer, or in a browser. You can also run the XSLT processor in debugging mode, setup breakpoints, run step by step, view local and global XSLT variables, and many more.