libusb-win32 is a Windows port of the (now deprecated) USB library libusb-0.1
libusb-win32 is a port of the USB library libusb-0.1 (https://sourceforge.net/projects/libusb/) to 32/64bit Windows. The library allows user space applications to access many USB device on Windows. (https://sourceforge.net/projects/libusb-win32/)
There are two versions of the libusb API: the current libusb-1.0 API, and its legacy predecessor libusb-0.1. (http://www.libusb.org/#Gettingstarted)