Indeed, I'm personally half of a two-dev team maintaining and developing a system that I'd say falls deep into this category. Our giant legacy codebase has a fe

Indeed, I'm personally half of a two-dev team maintaining and developing a system that I'd say falls deep into this category. Our giant legacy codebase has a few warts, but on the whole it follows a few simple design patterns that, once you understand them, makes it very easy to find your way around and change/extend. We also have an extensive domain understanding and direct contact with our user base, so we design, implement, review/test and deploy features very fast compared to any other team I've encountered in the organization. And though the underlying technology is mostly ancient, our product is growing strongly and consistently outcompeting systems with budgets of a different stratosphere in the open market.