Okular, the unified document viewer
git clone git://anongit.kde.org/okular.git
Okular is the successor of kpdf, the PDF viewer in KDE 3.
kpdf was refactored and extended in a Google Summer of Code project to support not only viewing PDF but also other types of document, e.g. PostScript files, images and many more.
KDE's Doxygen guidelines are available online.