It's honestly short and pretty unique.

He wrote a programming language for his master thesis, so obviously he used it to write all his software. His first project was the POS/management system for his father's music store (Now famous as the Mexican company that acquired Sam Ash). I believe they didn't switch until around 2005 or so (so about 30 years maintaining it or training a software developer on it as a side thought)

He then started a large sized customs software company with i that ended up getting acquired.. Everytime the language required a new feature the devs would just ask him (like when he had to write a graphical toolkit for it because it started as a text only runtime). There is no record of this language anywhere as far as I know.

I believe around the 2000s as part of the sale of the company he rewrote the whole stack in C#. And he's been using it ever since, including the company we started together in 2013 (together doing a lot of work here). Still with good old Notepad and CSC.exe just like year 1.He curses everytime the ecosystem has big required changes (async, nuget) though I've managed to coerce him into keeping up with the times, dragging and screaming.