We've heard about three-tier application design most of our professional lives, but what we don't often talk about is that, while every app has all three tiers, most applications care a lot more about one tier than the others. That's fine, if not good, but a good workflow solution should not look like a good tracking system or a good mobile app. They need different things, they work different ways, and you should approach them in different ways. It's not about one approach being better than another; it's about using the right approach for the right use case. We'll go through principles and examples.