You can dig into the source code for Original Apollo 11 guidance computer (AGC) source code for Command Module (Comanche055) and Lunar Module (Luminary099). Digitised by the folks at Virtual AGC and MIT Museum in this GitHub repository. This source code has been transcribed or otherwise adapted from digitised images of a hardcopy from the MIT Museum. The digitisation was performed by Paul Fjeld, and arranged for by Deborah Douglas of the Museum. Many thanks to both.
The AGC’s source code is an excellent example of organising a large and complex codebase. Written in an assembly language, the code is impressively well-structured. Tasks are split into separate modules and routines for better maintainability, a practice that is even more vital in today’s complex software projects.
https://www.bytelimes.com/what-we-can-learn-from-the-code-that-took-us-to-the-moon/