From http://en.wikipedia.org/wiki/Mapnik
Mapnik is an open source mapping toolkit, written in C++ and useful for both desktop- and server-based map rendering. One of its many users is the OpenStreetMap project (OSM) which uses it in combination with an Apache Web Server module (mod_tile) to render tiles that make up the OSM 'Slippy Map' Layer[2]. An XML file can also be used to define a collection of mapping objects that determine the appearance of a map, or objects can be constructed programatically in C++, Python, and Node.js. Artem Pavlenko, the original developer of Mapnik, set out with the explicit goal of creating beautiful maps[3] by employing the subpixel anti-aliasing of the Anti-Grain Geometry (AGG) library. Mapnik now also has a powerful Cairo rendering backend. When it comes to handling common software tasks such as memory management, filesystem access, regular expressions, and XML parsing, Mapnik utilizes the Boost C++ Libraries.