In the 1980s I got a lot of mileage out of the open source OPS5 expert system tool, porting it to my Xerox 1108 and eventually to the product ExperOPS5, and use

In the 1980s I got a lot of mileage out of the open source OPS5 expert system tool, porting it to my Xerox 1108 and eventually to the product ExperOPS5, and used it in house for prototyping. My one weekend project: while my wife was out of town with the kids for a weekend, I manually converted about 4500 lines of Common Lisp code to MIT Scheme, and it worked after a few hours of debugging. Another weekend project: I used my company’s time sharing system to write a very simple Chess program in FORTRAN in one weekend. It didn’t quite play a legal game, no en passant capture. Several months later when I purchased serial number 71 Apple II, I ported the code to Apple Basic, which only took a few hours. Apple distributed that little hack with their Apple II demo program cassette tape.