mod_mmap_dynamic is a reverse caching solution for the Apache Webserver. Its requires Apache 1.3.24 or higher and currently requires Linux kernel headers for test and set. It may compile on other OS's if you copy asm/atomic.h and satisfies its #includes.
It uses either Apache Internal Redirects to generate content from another module (PHP, JSP etc) or uses mod_proxy to generate content from remote servers.
Caching is done in memory using a hashtable and content is also compressed before being served to the user. Since content is only compressed once for everytime it is generated this minimises load from compression.
Current version is 0.1. It appears relatively stable but there are issues with directory handling if you are not using mod_proxy.
Current version is here.
Documentation in text format here.