Q: Does libopenraw works on Windows?
A: it should, but the developers do not have the will or the mean to even try out. libopenraw is written using standard C++ and portable libraries (boot, libjpeg) so it shouldn't be a problem.
Q: What APIs does libopenraw provide?
A: Currently only APIs to extract thumbnails or previews, and to extrace the CFA data, decompressed or not (notable exception is NEF). More is to come.