AllegroServe
Portable AllegroServe is a portable version of Franz Inc's AllegroServe HTTP server, which also includes an HTML generator and an HTTP client.

It supports Xanalys LispWorks, CMUCL, MCL, OpenMCL and Corman Lisp.

You can find it at http://sourceforge.net/projects/portableaserve, and the best way to load it into a project (as with most CL libraries these days) is via Quicklisp.

AllegroServe (formerly Allegro iServe) is a LLGPLed Web server which is designed for use with Allegro Common Lisp.

AllegroServe has a public repository and online documentation that includes a tutorial.

NOTE - Portable Allegroserve has been maintained with patches recently, for compatibility with LispWorks, SBCL/Linux, and CCL. At some point it could use a refactoring for acl-compat to use now-defacto-standard libraries from Quicklisp (e.g. Bordeaux-threads), and to track the current original AllegroServe. But the current Portable AllegroServe is usable at least on the platforms mentioned.