ABC was Python's most direct predecessor; I worked on it from around 1983-1986.
I downloaded these sources from cwi.nl, specifically the abc-unix tarball.
Another copy of the ABC sources lives in Luciano Ramalho's GitHub. I hope one day to compare the two trees and unify them.
Most files have 1991 as their latest modification time in the tar ball; a few have 1996 or 2021.
The old README file has build instructions.
The current sources assume a 32-bit system where int and pointers have the same size. I hope to eventually upgrade the source code to work on 64-bit systems too (where int is 32 bits and pointers are 64 bits).
CWI never put a license on ABC, but it says:
Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1988-2011.
I'll try to negotiate with Steven Pemberton eventually (hopefully MIT).
Eddy Boeve, Frank van Dijk, Leo Geurts, Timo Krijnen, Lambert Meertens, Steven Pemberton, Guido van Rossum.
- Leo Geurts, Lambert Meertens and Steven Pemberton, The ABC Programmer's Handbook, Prentice-Hall, Englewood Cliffs, New Jersey, 1990, ISBN 0-13- 000027-2.
- Steven Pemberton, An Alternative Simple Language and Environment for PCs, IEEE Software, Vol. 4, No. 1, January 1987, pp. 56-64. http://www.cwi.nl/~steven/abc.html
- Steven Pemberton's home page. https://homepages.cwi.nl/~steven/abc/
- Lambert Meertens, The Origins of Python. https://inference-review.com/article/the-origins-of-python