CERN httpd
No longer maintained, but possibly of historical interest.
http://www.w3.org/Daemon/

Common Lisp Hypermedia Server: CL-HTTP
A highly portable http/1. 1 server which supports cgi, server-side lisp programs, java, javascript.
http://www.ai.mit.edu/projects/iiip/doc/cl-http/home-page.html

PicoWeb
Product description, news, support pages.
http://www.picoweb.net/

Pi3Web
Supports CGI, FCGI, ISAPI, PHP4, SSL. Free binary or source downloads, documentation, mailing list, FAQ, screenshots. [Windows, Linux]
http://pi3web.sourceforge.net/pi3web/

Aestiva
The HTML/OS product enables web designers to build advanced dynamic sites w/out CGI programming. For Unix and NT servers. ISP-friendly.
http://www.aestiva.com

Zeus Web Server
Solutions for content providers, ISP hosting, intranets and secure e-commerce with support.
http://www.zeus.com/

Tcl Web Server
A pure-Tcl web server.
http://tcl.activestate.com/software/tclhttpd/

The SRE-http project
dedicated to the provision of free, WWW-aware software to the OS/2 community. Written primarily in REXX, theflagship product is the SRE-http http/1.1 server for OS/2.
http://www.srehttp.org/

kHTTPD for Linux
An http-daemon webserver for linux. Khttpd is different from other webservers in that it runs from within the linux-kernel as a module device-driver.
http://www.fenrus.demon.nl/

Voyager Server
For QNX OS and/or embedded devices.
http://www.qnx.com/products/photon/internet.html

Micro_httpd
Implements all basic web server features in only 150 lines of code.
http://www.acme.com/software/micro_httpd/

NCSA HTTPd
No longer supported, site still includes documentation.
http://hoohoo.ncsa.uiuc.edu/

Netcraft
A list of servers. Also a survey of webserver software usage.
http://www.netcraft.com/survey/servers.html

NetCloak
Web server enhancement package that allows you to create interactive, dynamic web sites. Running as either a stand-alone CGI application or as a high-performance WebSTAR API plug-in.
http://www.maxum.com/NetCloak/

fhttpd
FTP/HTTP server with modules support. Modules run as separate "looping" processes locally or remotely, and can be configured to run under separate userids.
http://www.fhttpd.org

SQLData Desktop Server
A powerful web database server that allows user to access ODBC data sources using a web browser. Now you can have your own database server with no CGI or programming.
http://www.sqldata.com/desktop.htm

Zilog: EZ80 Webserver
Overview of chip-based Z80S183 Advanced Mixed Signal System and Z80S188 Advanced Embedded Microprocessor. Technical documentation and support pages.
http://www.zilog.com/ez80/

InstantServers
Desktop Web hosting solution. Documentation and technical specifications available. [Windows]
http://instantservers.com/

Secure Web Server for S/390
HTTP/HTTPS server for OS/390, MVS, and VM offers fully secure web site hosting on the mainframe as well as direct dynamic web access to any 3270 application. MVS and VM fact sheet available in PDF format.
http://www.informationbuilders.com/products/web390/

A Model of Web Server Performance
PDF and HTML versions of this article, with a forum. By Louis P. Slothouber, Ph.D.
http://www.geocities.com/webserverperformance/

Mac Web Server and BBS
Operator Headgap Systems is the Worldwide Distributor for TeleFinder Internet BBS and Server Software. Full documentation, ordering and update information.
http://www.Mac-WebServer.com

Center for Information Technology Integration: Webcard
Based on a Schlumberger Cyberflex Access Java Card. Testdrive, technical report, press releases, source.
http://www.citi.umich.edu/projects/smartcard/webcard/

Netcraft: Web Server Survey
Web tool retrieves hosting software information from any domain name.
http://uptime.netcraft.com/

Newton Personal Data Sharing
A web server for a NewtonOS 2.x device.
http://npds.free.fr/

Small Web Servers
Contains information on three projects, webACE, webACE II (very small web servers) and Spud (a potato-powered web server ).
http://d116.com/

HTTPi
Small-footprint server offering executables, server-parsed pages, access control and virtual hosting (perl).
http://www.floodgap.com/httpi/

Abyss Web Server
A free and small personal web server for Windows and Linux supporting HTTP/1.1 and CGI. Features a remote web management interface.
http://www.aprelium.com/abyssws/

Roxen Webserver
Web server and application server which includes support for RXML, a tag-based language for constructing dynamic content. Allows tag plugins to be written in Pike.
http://www.roxen.com/products/webserver/

ghttpd
A fast and efficient HTTP server that has CGI support (no post support, only get). Ghttpd has a small memory footprint and is capable of handling thousands of simultanious connections. GPL.
http://gaztek.sourceforge.net/ghttpd/

Web Server/400
A native AS/400 application that takes full advantage of the latest IBM OS/400 V3R1 offerings, and provides all of the features of the most popular current Web servers.
http://www.inetmi.com/iseries/webserver/

Xs- Httpd
Small and fast WWW server with many features.
http://www.stack.nl/~johans/xs-httpd/

Phttpd
Lightweight multithreaded solution. Partial documentation, free source download. [Solaris]
http://www.theo-physik.uni-kiel.de/phttpd/

WN
Web server that runs on a variety of Unix platforms and is free under the terms of the GNU General Public License. Online user guide, and other documentation.
http://hopf.math.northwestern.edu/

Plesk Server Administrator
World-class, innovative new product designed to make web server management easier for everyone.
http://www.swsoft.com/plesk