Too Long; Didn't Read
A few years ago, Ron Burkey released the source code for the Apollo Guidance Computer, or AGC. The AGC source code is written in assembler, which is foreign to most of us. It's a rabbit hole for geeks, but perusing through a lot of this source code, you can piece together how some of this stuff works. For the 50th anniversary of the Apollo 11 Moon Landing, Simon Allardice created an awesome course on Pluralsight exploring the system.