Mapnik is a toolkit for developing GIS applications. At the core is a C++ shared library providing algorithms/patterns for spatial data access and visualization. Essentially a collection of geographic objects (map, layer, datasource, feature, and geometry), the library doesn't rely on "windowing systems" and can be deployed in any server environment. It is intended to play fair in a multi-threaded environment and is aimed primarily, but not exclusively, at Web-based development. High-level Python bindings (boost.python) facilitate rapid application development, targeting zope3, django, etc.
Qanava is a C++ library designed to display graphs on a Qt canvas. Qanava provide classes to generate various layouts of directed graphs and visualize their nodes with custom styles on a graphic canvas. Qanava is designed for applications with basic graph visualization needs such as Gantt charts, social networks, and document or network modelling applications. It is not meant for a complex interactive visualization of very large data sets.