Yes - pinball.sys - was a reghack on 3.51 - and it still worked on NT 4.0 - although "this is not supported" yada yada. I had a machine that quintuple booted various Windows and OS/2 versions - HPFS always impressed me with its speed.
One of our old and missed members, Brad Barclay (aka Yazstromo, OS/2 god), wrote a nice summary of HPFS here some years ago.