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.
mod_log_spread is a patch to Apache's mod_log_config, which provides an interface for spread to multicast access logs and per-vhost logs. It utilizes the group communication toolkit Spread for reliable multicast transport. mod_log_spread was developed to solve the problem of collecting consolidated access logs for large web farms. In particular, the solution needed to be scalable to hundreds of machines, utilize a reliable network transport, allow machines to added or dropped on the fly, and impose minimal performance impact on the Web servers.
mod_ntlm is a NTLM authentication module for Apache / Unix. NTLM is often used in Microsoft based Intranets to pass user's credentials from their workstation-logon to the web server (user authentication without password boxes). Password validation is done through Windows NT or Samba machines over TCP/IP.
The Apache/Perl integration project brings together the full power of the Perl programming language and the Apache HTTP server. With mod_perl it is possible to write Apache modules entirely in Perl. In addition, the persistent interpreter embedded in the server avoids the overhead of starting an external interpreter and the penalty of Perl start-up time.
mod_proxy_add_forward.c is an Apache module that adds a 'X-Forwarded-For' header to outgoing proxy requests like Squid does. You can then get the client IP back on the proxied host by setting r- >connection->remote_ip from this header. It's very useful for the common lightweight frontend/heavy backend mod_perl setup.
mod_repository turns Apache into a content storage system with the benefit of storing just one copy of each file submitted to the repository. Upon storing a file a user is given a unique token representing the file. This can be used to create content servers which are abstracted from the filesystem. Files can be placed, retrieved, and deleted from the server.
With mod_roaming you can use your Apache webserver as a Netscape Roaming Access server. This allows you to store you Netscape Communicator 4.5 preferences, bookmarks, address books, cookies etc. on the server so that you can use (and update) the same settings from any Netscape Communicator 4.5 that can access the server.