mod_vhs is an Apache 2.2+ Web server module allowing mass virtual hosting without the need for file-based configuration. The virtual host paths are translated from any database supported by mod_ldap or mod_dbd at request time from MySQL, LDAP, PAM, or a system password file. PHP security can be basically auto-configured from the database using this module. Requests are cached by mod_ldap when configured.
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_sphinx is an Apache module which intercepts output bound for the client, whether it be from files served by the same Web server, files sent via reverse proxying, or files delivered by transparent forward proxying (outbound proxying, as in your browser's proxy setting). It opens the text and replaces a word with another word or phrase. When in regular proxy mode, it cannot modify SSL content since Apache cannot decrypt that (it would be a protocol violation).