"KLH10" is an emulator for the PDP-10 series of machines from Digital Equipment Corporation. The most important thing to know is that this is a MACHINE emulator. It emulates a specific PDP-10 CPU and all necessary I/O devices, running a site's existing operating system (monitor) binary without change -- which then runs user-mode application programs just as if they were on a real PDP-10. Even floating-point results are bit-identical.
KLH10 was created by Kenneth L. Harrenstien. Its homepage is http://klh10.trailing-edge.com/