Web/Deploy
Deployment/Backend options for your haskell web code.
Happstack
includes its own server. see Web/Frameworks
Yesod
Yesod targets WAI backends. See WAI + FastCGI below for another option. The premier WAI backend is the Warp web server. see Web/Frameworks
(Fast)CGI + WAI
Use a webserver like nginx, lighttpd, or Apache. These servers would communicate with your web applications using CGI or FastCGI. See wai-handler-fastcgi for a library which connects FastCGI with the WAI interface. A search for wai-handler shows the various options available. See the deployment chapter of the Yesod book to see how to configure the various servers and FastCGI to host WAI applications.
Snap
includes its own server. see Web/Frameworks
(Fast)CGI
Use CGI or FastCGI to talk to another web server. See this tutorial on simple CGI programming for a simple example.
Other
Check out the documentation for others frameworks listed at Web/Framework