mod_asn is an Apache module that uses BGP routing data to look up the autonomous system (AS) and the network prefix (subnet) which contains a given (client's) IP address. mod_asn is highly scalable. To do lookups in high-speed, it uses the PostgreSQL ip4r datatype, which is indexable with a Patricia Trie algorithm to store network prefixes. This is the most suitable algorithm, being able to search through around 250,000 existing prefixes quickly. mod_asn is usable as a standalone module, and the lookup result can be used by scripts or other Apache modules. For instance, a download redirector could base its decisions on the lookup result provided by mod_asn.
mod_athena is an Apache-based application load balancer for large systems. It allows the HTTP server to act as a load balancer either internally to Apache's own mod_proxy (for reverse proxying), or externally to machines querying it. Arbitrary statistics are sent to the engine via a simple GET plus query-string interface, from which it will then make decisions based on chosen algorithms.
mod_auth_useragent2 is an Apache module that can be used to limit access to documents by means of the User-Agent. As an authentication method, this is really unsafe because it is easy to change the User-Agent in most browsers, but it could be used to prevent stupid bots and spiders from accessing your Web sites.
The mod_cidr_lookup is an Apache module for version 2.2 and 2.0. The mod_cidr_lookup detects client type by looking up the client's source IP address in CIDR blocks. This module sets the environment variable X_CLIENT_TYPE and the HTTP request header X-Client-Type, so it can be used in both Apache (httpd.conf) and Web applications.