Abstract: kaChing powers the largest social investment site on the web with nearly 500,000 registered users. Our mission is to make the investment world open by offering transparent investment vehicles that directly compete with mutual funds. Over the past year and a half, we have built a large feature set and evolved our software continuously with very short iterations and (almost) no regression. In this talk, I will present our experience building a large test-driven code base from the ground up. Using concrete examples, we will have a look at component based APIs, declarative programming, minimizing the concepts of an API, specific cases of separation of concern and interactions with third-party software. We will look at multiple programming paradigms from languages such as Scala, shell script and Prolog and see how these ideas can be embedded as syntactic sugar in your Java.