I definitely admired PostgreSQL's code when I first looked at it. Projects written in C require a fair amount of care and discipline to be scaled up to larger

I definitely admired PostgreSQL's code when I first looked at it. Projects written in C require a fair amount of care and discipline to be scaled up to larger codebases and teams. PostgreSQL is such a codebase. I've also seen various parts of Spring's codebase and found all of it to be consistently solid and careful. They take a lot of care to structure carefully and comment immaculately. Disclosure: I work for Pivotal, which sponsors Spring. Which is why Spring is highly visible in my working life.