Software

AllegroServe
Web application server to embed in Common Lisp programs. [Open Source, LGPL]
http://allegroserve.sourceforge.net/

cCLan
A project to package and easily distribute Lisp software. It is loosely modelled after the ideas behind CPAN, for Perl.
http://cclan.sourceforge.net/

CL-EMB
A library to embed Common Lisp and special template tags into normal text files. Can be used for dynamically generated HTML pages. [Open source, Lisp Lesser General Public Licence]
http://common-lisp.net/project/cl-emb/

CL-GD
A library for Common Lisp which provides an interface to the GD Graphics Library for the dynamic creation of images. It is based on UFFI and should thus be portable to all CL implementations supported by UFFI. [Open source, BSD-style license]
http://weitz.de/cl-gd/

CLiki
Interactive, collaborative Wiki dedicated to Common Lisp. Large amount of diverse information.
http://www.cliki.net/index

CL-Interpol
Library for Common Lisp, modifies reader to have interpolation within strings similar to Perl or Unix Shell scripts; gives various ways to insert arbitrary characters into literal strings even if editor/IDE doesn't support them. [Open source, BSD-style license]
http://weitz.de/cl-interpol/

Closure Web Browser
Free, written in Common Lisp only; description, download.
http://www.stud.uni-karlsruhe.de/~unk6/closure/

CL-PPCRE
A portable Perl-compatible regular expressions for Common Lisp. [Open source, BSD-style license]
http://weitz.de/cl-ppcre/

CL-WHO
A Lisp Markup Language, i.e. it provides convenient means to convert S-expressions intermingled with code into (X)HTML, XML, or whatever. [Open source, BSD-style license]
http://weitz.de/cl-who/

CL-WIKI
Wiki engine for Common Lisp. Runs alone or on Apache + mod_lisp. [Open source, Lisp Lesser General Public License]
http://common-lisp.net/project/cl-wiki/

CLX
An interface between Common Lisp and X Window.
ftp://ftp.cs.cmu.edu/afs/cs/project/ai-repository/ai/lang/lisp/gui/clx/0.html

CL-XML
James Anderson's collection of Common Lisp modules for XML includes XQuery support.
http://pws.prserv.net/James.Anderson/XML/

Common Lisp Music
A music synthesis and signal processing package in the Music V family.
http://ccrma.stanford.edu/software/clm/

Foil: Foreign Object Interface for Lisp
Protocol and libraries that help access common object runtimes (JVM, CLI/CLR (.MET)) and their libraries, from Lisp. Open source, Common Public License.
http://foil.sourceforge.net/

Fractal Concepts: Maintainer of mod_lisp and cl-pdf
mod_lisp is an Apache plugin which lets apache send requests to a lisp process to generate dynamic content. Think of it as java server pages for lisp. cl-pdf is a library to create files in Portable Document Format from Common Lisp.
http://www.fractalconcept.com/

Garnet
A user interface development environment for Common Lisp and X11 or Macintosh. It helps you create graphical, interactive user interfaces for your software.
http://www.cs.cmu.edu/Groups/garnet/

Genworks International
GDL Application Development System, dynamic Knowledge Base Language and Development Environment; Generative Web Language (GWL), an integrated web-based user interface platform, for rapid development and deployment of dynamic webserver-based apps. ANSI Common Lisp based.
http://www.genworks.com

Grasper-CL
Interactive Network Editor and Graphical Database.
http://www.ai.sri.com/~grasper/

HTML-Template
Portable library for Common Lisp, can be used to fill templates with arbitrary (string) values at runtime; loosely modeled after Perl module HTML::Template and compatible with a subset of its syntax. [Open source, BSD-style license]
http://weitz.de/html-template/

Hunchentoot
Web server coded in Common Lisp; supports HTTP/1.1 chunking, persistent connections (keep-alive), and SSL; works only with LispWorks.
http://weitz.de/hunchentoot/

Lisp for Robot AI Minds
Artificial intelligence in Lisp.
http://mind.sourceforge.net/lisp.html

lisp-cgi-utils
A software package for developing CGI scripts with Common Lisp. It implements a very basic HTTP/CGI interface (sending headers, getting GET/POST and environment variables) and offers tools for easier HTML generation with special support for handling HTML forms. [Open source, LGPL]
http://www.thangorodrim.de/software/lisp-cgi-utils/index.html

McCLIM
An open source implementation of the Common Lisp Interface Manager, a portable and standardized library for constructing user interfaces.
http://common-lisp.net/project/mcclim/

RDNZL
A .NET layer for Common Lisp. Lets CL programs interact with .NET libraries. Open source, BSD-like license.
http://weitz.de/rdnzl/

TBNL
A toolkit for building dynamic websites with Common Lisp. It employs the popular Apache web server for the actual HTTP communication between the server and the browser and it uses Marc Battyani's mod_lisp for the communication between Apache and the Lisp image. [Open source, BSD-style license]
http://weitz.de/tbnl/

URL-Rewrite
Small package, can be used to programmatically rewrite (X)HTML documents, to replace some attribute values by others. Description, code samples, downloads, links. [Open source, BSD-style license]
http://weitz.de/url-rewrite/