What programming language did you use for the Teudogar engine?
I wrote the Teudogar Engine in C++: about 140,000 lines or 2,400 pages of C++ code; printed on endless paper, that’d result in a 650 yards / 600 meter paper trail. With that language (and a clean, disciplined programming style), I found it sufficiently easy to keep control of all this code, to keep it work interdependently, and to keep the entire project reasonably bug-free (in spite of this project’s size, the final 1.00 release contained only three or four very minor bugs).