During the Shuttle program, the Shuttle Avionics Integration Laboratory (SAIL) was used for training purposes and to integrate changes to hardware and flight software into the orbiters. Containing 100% accurate cockpit and avionics, SAIL was identified as OV-095. I didn't know this, but the trainers were all given OV (Orbital Vehicle) identifiers. Numbers below 100 indicated it was not flight worthy. The SAIL is basically the guts of a Shuttle without its outer shell.
This Fall, SAIL will re-emerge as a tram stop on the Space Center Houston tour.