auth_ldap is an LDAP authentication module for the Apache Web server. Auth_ldap has excellent performance, due to its use of aggressive client-side caching algorithms. It also has support for LDAP over SS or TLSL. It also features a mode that lets Microsoft Frontpage clients manage their Web permissions while still using LDAP for authentication.
Jigsaw is W3C's leading-edge Web server platform, providing a sample HTTP 1.1 implementation based on RFC2616 and a variety of other features on top of an advanced architecture implemented in Java. Jigsaw provides both client and server HTTP/1.1 implementations, is fast, easy to extend, flexible, and is also packaged as a ready-to-run HTTP/1.1 proxy-cache.
mod_backhand is a load balancing module for Apache. It provides per-request HTTP redirection within a heterogeneous Apache server cluster. Each request is processed and run through a set of "candidacy functions" to determine which server is best suited to respond. The request is then proxied to that server. Facilities are in place to allow you to write your own dynamically loadable decision making algorithms. Everything about the request and the current availability of resources can be used in the decision-making process.
mod_dav enables Apache to understand the WebDAV protocol (extensions to HTTP). WebDAV stands for "Web-based Distributed Authoring and Versioning", and is defined by RFC 2518. WebDAV is intended to replace proprietary authoring protocols such as those used by Frontpage or NetObjects' Fusion, but is also a complete set of protocols for manipulating a webserver's files and directories, and their properties.
mod_layout is an Apache module that provides both a Footer and Header directive to automagically include output from other URIs at the beginning and ending of a Web page. It can be used to wrap documents for a standard look and feel for a site (or to insert banners on any given document in a site). Currently known to support mod_perl, PHP and Apache JServ. Should support just about any type of handler.