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 utilises best of breed industry standard libraries from boost.org