Unified process, which, despite usually not being called that way and/or being codified in the way it is nowadays, is how virtually all early software companies did their development work post-punchcards (when you no longer had to get things done in a single step).

It's why the "agile is better because iterative hoooo!" is so laughable, because even though we didn't yet call it iterative - as a distinction from pre-planned, since we thought in punchcards+mainframe vs after that - we did iterative work. Of course we did, software development is naturally iterative and Waterfall was the contrived contrasting example of how a non-iterative process would look.