The libusb project has been around for more than a half-decade to serve as a cross-platform, user-mode library providing generic access to USB devices. The open-source USB library has even been ported to Windows. However, it's been forked by some unhappy developers.
The libusbx project has been spawned as the fork reportedly because of the upstream maintainer not dong any stable releases in more than a year and a half. The maintainer was also slow with merging new code and other work. As a result, several upstream libusb developers forked and created libusbx.
The libusbx code is working on new features that libusb doesn't support like USB topology, HID, and hot-plugging.
This fork isn't brand new, but it's getting brought up now because libusbx is expected to go into Fedora and its gaining traction elsewhere. It's talked about in this blog post.
Those wishing to learn more about libusbx can visit the SourceForge project site.