XGeoIP is an Apache2 module that implements geo-localization, based on the remote client IP address. It relies on MaxMind GeoIP databases for efficient IP addresses lookup (i.e. you need to download either a free "limited", or buy a complete "accurate" version of one of their databases). Since MaxMind already provides an Apache module, the rationale behind this development may look tweaked somehow, but this module provides unique features that the original module from MaxMind doesn't:
GeoIP C library independence: the XGeoIP module is completely self-contained, and does not depend on third-parties libraries (the databases traversal algorithm was re-implemented directly in the module)
Memory model: whereas the original module databases lookup is either file- or shared-memory-based, the XGeoIP module uses mapped memory for efficiency in a multi-processes parent/child environment (like the traditional forked MPM in Apache2)
Performance: using the memory mapped strategy, only needed databases blocks are loaded (and cached by the OS VM) during databases traversal; these blocks are instantaneously available to all Apache processes. Also, mapped memory is generally faster than shared memory on most OSes.
Secured proxy support: when the actual web server is located behind a (reverse) proxy, the received IP address is the proxy's and not the originating client's. The XGeoIP module provides support for retrieving the originating client IP address through an HTTP header, only sent from authorized proxies (to avoid potential IP spoofing attacks).
Secured information cache cookie: IP addresses lookup may be expensive on busy web servers (even if the MaxMind algorithm is actually very fast). The XGeoIP module provides support for a secure "cache" session cookie containing the geo-localization information from the first databases lookup: this cookie will be passed back and forth between the client browser and the server, speeding up geo-localization information retrieval (no databases traversal will be involved as long as the client session lasts and its IP address doesn't change).