Cairo
Cairo is a free software 2D graphics library. It is vector-based, and can be used to produce SVG and PDF format images, for instance. It is cross-platform (Linux, Mac, and Windows). Cairo is used as the rendering engine in the latest version of the Firefox browser (and as such cairo-produced SVG graphics are implicitly well suited for display in Firefox).
Python
Installing on Debian
sudo apt-get install python-cairo