Poppler is librarified PDF rendering toolkit derived from the Xpdf 3.0 code base. It can utilize X11-independent rendering backends like Cairo, Splash, or Qt4 Arthur. It's not designed for platform-agnosticy, but proper BSD/Linux integration; is used by various PDF applications (Evince, Okular, TeXStudio, pdftotext, Zathura, Xournal, Inkscape), and comes with a set of command-line tools of its own.
Bokeh is a Python library for interactive visualizations, plots and dashboards in web browsers. It provides unique rendering recipes and capabilities for large and streaming data sets.
wxSVG is C++ library to for Scalable Vector Graphic (SVG) files. It can create, manipulate and render them using the wxWidgets toolkit.
Nux is a OpenGL-based widget toolkit, with some functional resemblence to Gtk+. It's developed and used by Ubuntus Unity. It's comprised of three libraries: NuxCore for types/math/color/urility functions, NuxGraphics abstracts the rendering and canvas interaction, and Nux itself providing the widgets atop.
Geomview is an interactive 3D viewing program for Unix. Geomview lets you view and manipulate three-dimensional objects: you use the mouse to rotate, translate, zoom in and out, and so on. Geomview can be used as a standalone viewer for static objects or as a display engine for other programs which produce dynamically changing geometry. Geomview can display objects described in a variety of file formats. Geomview comes with a wide selection of example objects, and you can create your own objects