Ask HN: What is the FOSS project with the worst code quality?

I was having a discussion with a friend yesterday and realized that there aren't really any good resources with examples of bad code that actually does something useful. I'm sure there is plenty of terrible code on GitHub that is technically FOSS, but what is the worst among projects which actually see moderate to widespread use?

Note that this is very informal and for entertainment. Authors of FOSS software, we all love what you do! At the end of the day, what really matters is if the code is solving the problem it was intended to solve.

To start things off, I've found the Gradle code base to be very difficult to navigate. It's a great build system, but actually figuring out where functionality is implemented is very difficult.