Not mind blowing, but calling a subroutine BURNBABY in your moon launch code is just great.

https://github.com/chrislgarry/Apollo-11/blob/a13539c7c5c482...

Also finding out the source was similar to open source quad copter code with perhaps one the first usages of a Kalman filter to integrate various instruments to maintain level flight was both mind blowing and very satisfying.

Not only can you read it, you can also run it!

https://www.ibiblio.org/apollo/index.html