From the FAQ:
What is mapnik?
Mapnik is a Free Toolkit for developing mapping applications. It’s written in C++ and there are Python bindings to facilitate fast-paced agile development. It can comfortably be used for both desktop and web development, which was something I wanted from the beginning.
Mapnik is about making beautiful maps. It uses the AGG library and offers world class anti-aliasing rendering with subpixel accuracy for geographic data. It is written from scratch in modern C++ and doesn’t suffer from design decisions made a decade ago. When it comes to handling common software tasks such as memory management, filesystem access, regular expressions, parsing and so on, Mapnik doesn’t re-invent the wheel, but utilizes best of breed industry standard libraries from boost.org
Which platforms does it run on?
Mapnik is a cross platform toolkit that runs on Windows, Mac, and Linux (Since release 0.4). Users commonly run Mapnik on Mac >=10.4.x (both intel and PPC), as well as Debian/Ubuntu, Fedora, Centos, OpenSuse, and FreeBSD. If you run Mapnik on another Linux platform please add to the list on the Trac Wiki
What data formats are supported?
Mapnik uses a plugin architecture to read different datasources. Current plugins can read ESRI shapefiles, PostGIS, TIFF raster, OSM xml, Kismet, as well as all OGR/GDAL formats. More data access plug-ins will be available in the future. If you cannot wait and/or like coding in C++, why not write your own data access plug-in?
What are the plans for the future?
As always, there are lots of things in the pipeline. Sign up for the mapnik-users list or mapnik-devel list to join the community discussion.
Governments as well as NGOs need mapping applications.
What mapping application will you create? What data will it merge on the fly for your users?