See page 167ff in https://www.amazon.com/Unix-Programming-Environment-Prentice-Hall-Software/dp/013937681X for 3 scripts that do rudimentary revision control (RC).
I have worked a little with gnu-arch (aka "tla"), http://savannah.gnu.org/projects/gnu-arch/ , it is no longer maintained, but still available.
As noted by Richard Chambers, RCS is available (as is cssc, an sccs clone in Linux repositories).
Eric Raymond has written "src", a python code: http://www.catb.org/~esr/src/ -- I have an early version, but have not had time to test it. I'm guessing that this may be your best bet.
(At our shop we use numerous levels for backup as well as RC. For example, we wrote a wrapper around rcs to simplify behavior for small projects and a development edition that uses bzr in place of rcs. I have more than 700 RCS directories in my tree of projects. For systems, we use VM snapshots, and for daily backup, rsnapshot.)
For a much longer list, see https://en.wikipedia.org/wiki/Comparison_of_version_control_software
Good luck ... cheers, drl