Originally Posted by NorthWay
Erm... was that a rhetoric question?
Anything multiuser probably. Unixen, VMS, MVS. GECOS?
Not sure about OS-9. Probably not Lisa.
Don't forget Mac OS. It used a "handle" mechanism for tracking (essentially a indirection of pointers). I would be surprised if Lisa didn't use the same mechanism.
Also QNX, DESQview (at least partially) and IIRC even the original GEOS.