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).
Lisp Blosxom is a port of the Perl Blosxom blogging engine to ANSI Common Lisp. Its goals are extensibility and speed. It's a filesystem-based blogging engine, which means that blog entries are just flat files on disk, although plugins can be written to extend or replace this behavior. The first line in the file is the title, while the remainder is the text of the body. Entry dates are taken directly from the filesystem's modification date for each entry. Furthermore, the structure of the blog is taken directly from the hierarchy of directories and files on disk.
Steel Bank Common Lisp is a development environment for Common Lisp, with excellent support for the ANSI standard: garbage collection, lexical closures, powerful macros, strong dynamic typing, incremental compilation, and the famous Common Lisp Object System (multimethods and all). It also includes many extensions, such as native threads, socket support, a statistical profiler, programmable streams, and more. These are all available through an integrated, interactive native compiler which feels like an interpreter. SBCL is unique in being a multiplatform native compiler which bootstraps itself completely from source, using a C compiler and any other ANSI Common Lisp implementation.
ACL2 is a mathematical logic, programming language, and mechanical theorem prover based on the applicative subset of Common Lisp. It is an "industrial-strength" version of the NQTHM or Boyer/Moore theorem prover, and has been used for the formal verification of commercial microprocessors, the Java Virtual Machine, interesting algorithms, and so forth.