ILISP is a package that is designed to integrate various Lisp implementations (mostly Common Lisp systems and various Scheme dialects, including Guile) within Emacs (or XEmacs). ILISP runs an inferior Lisp process (in Emacs parlance) and provides a specialized set of commands, key bindings, and menus to ease the interaction with it. ILISP commands access the underlying Lisp process and provide ways to make the editing, compilation, and execution of Lisp programs much easier.
CL-PPCRE is a portable regular expression library for Common Lisp. It is compatible with Perl, and it's fast, portable (strictly ANSI-compliant), and thread-safe. It comes with convenient features like a SPLIT function, a couple of DO-like loop constructs, and a regex-based APROPOS feature similar to the one found in Emacs. In addition to specifying regular expressions as strings like in Perl, you can also use S-expressions which are more Lisp-y.
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).
HTML-TEMPLATE is a portable library for Common Lisp that can be used to fill templates with arbitrary (string) values at runtime. It is intended to be used for HTML and is loosely modeled after the HTML::Template Perl module. It translates templates into efficient closures that can be re-used as often as needed, and uses an intelligent cache mechanism that allows templates to be updated while your program is running.
CL-INTERPOL is a library for Common Lisp which modifies the reader so that you can have interpolation within strings, similar to Perl or Unix Shell scripts. It also provides various ways to insert arbitrary characters into literal strings even if your editor/IDE doesn't support them.