Mapnik is a toolkit for developing GIS applications.

Mapnik is an OpenSource C++/Python toolkit for developing GIS (Geographic Information Systems) applications.

At the core is a C++ shared library providing algorithms/patterns for spatial data access and visualization.
High-level Python bindings (boost.python) facilitate rapid application development, targeting zope3, django.

The library doesn’t rely on “windowing systems”, it can be deployed in any server environment. The intention is to play fair in a multi-threaded environment and is aimed primarily at web-based development.

Some Key features :

• Â Extensible datasource plug-in architecture (ESRI shape files, PostgreSQL/PostGIS)
• Â Anti-aliasing rendering
• Â Expressions based styling

The New release has Some bug-fixes, better python integration, support for gcc4.

Reference:
Mapnik Home Page