This is a fluffy, non-technical article so I googled NTSYNC. It seems like they implement Win32 events, semaphores, mutex and WaitForMultipleObjects.

It's curious that they didn't do this as file descriptors that can be epolled. For example I think you could do semaphores and events with eventfd(2), which always struck me as inspired by those Win32 objects somehow. But maybe this is a simpler purpose built interface.