gLabels is a lightweight program for creating labels and business cards for the GNOME desktop environment. It is designed to work with various laser/ink-jet peel-off label and business card sheets that you'll find at most office supply stores.
Haru is a free, cross platform, open-sourced software library for generating PDF written in ANSI-C. It can work as both a static-library (.a, .lib) and a shared-library (.so, .dll).