http://libcrtxy.sf.net/
It is named after the so-called "X-Y" arcade game displays, such as the "Quadrascan" (created by Wells Gardner) and "Amplifone" monitors used in Atari vector-based games.*
I am creating this library with the intent to port a number of my own games (clones inspired by classic arcade games) to it: ICBM3D, Vectoroids, 3D Pong.
Helper functions are also included for doing fixed-point math (useful since your canvas size is not necessarily your screen size, and can be used for sub-pixel movement) and trigonometry (since most vector-based games involve things rotating).
(*) Names are trademarks of their respective trademark and copyright holders.