This is the project page of UniGrob (universal graphics objects), a 2D vector graphics library for OpenGL and D3D.
Its API is very similar to Cairo, for most functions you just have to replace "cairo_" with "ugo_".
Like Cairo, UniGrob is open source and licensed under the LGPL.
It is written in vanilla C.
You can get UniGrob via subversion.
svn co https://svn.sourceforge.net/svnroot/libufo/ugo/trunk ugo