The most remarkable legacy system I have seen
As the comment by timsworkaccount says, this is definitely Athena at JPMorgan.For those interested, I gave a talk on Athena at PyData UK 2018 called "Python at Massive Scale". 4500 developers making 20k commits a week. Codebase with 35m LOC.The video is here: https://www.youtube.com/watch?v=ZYD9yyMh9HkIt covers Athena's origins, what it is used for, application architecture, infrastructure, dev tooling and culture.