If you look back to NASA's 1969 Space Transportation System (STS) proposal ,you'll read all about space shuttles, as well as two bits of space tech that never made their way to reality: the nuclear space ferry and the space tug.
In this envisioned future, NASA would use space tugs (AKA orbital maneuvering vehicles) to move crew and cargo between different Earth orbits, but they'd also see use as lunar tugs between the moon's orbit and surface.
That's what we see in this 1970 illustration from an Gruman Aerospace Corp space tug concept:
The STS system would have seen astronauts leave the Earth for low orbit aboard a chemically-fueled shuttle. They'd dock with the space station and then tugs would provide transport to other orbits for satellite maintenance, etc. Finally the nuclear-powered NERVA would provide travel to the moon, where lunar tugs would handle local traffic.
Will space tugs and lunar tugs ever be a reality? The idea still comes up from time to time, but only time will tell. After all, if we scrapped it for budgetary reasons 40 years ago, what chances does it have today?