This is entirely dependent on what type of project it is. At most companies, tastes change over time so you end up with a hybrid of application layers built on

This is entirely dependent on what type of project it is. At most companies, tastes change over time so you end up with a hybrid of application layers built on different languages and technologies. I guess in an ideal world the stack would be as non-diverse as possible, but it never seems to end up that way.