I believe Stein used XtrkCad, a free-ware track planning program that runs on Linux, Windows, and some versions of Macintosh. Stein is no longer with us to answer.
I’m not sure what software Byron uses - he is a professional layout designer.
Fred W
Our late friend Stein used XTrackCAD. (As Fred noted). I use 3rd PlanIt.
Of course, CAD is not necessary to design a plan for oneself.
Byron
Very sorry to hear that. I ended up recreating it in Anyrail. I hope to build the 4x8. I believe it was from RRTrainMan