Comment by timr

Good question. No strict line, and it's always going to be subjective and a little bit silly to categorize, but when I'm debating this argument I'm thinking: a product that does not exist today (obviously many parts of even a novel product will be completely derivative, and that's fine), with multiple views, controllers, and models, and a non-trivial amount of domain-specific business logic. Likely 50k+ lines of code, but obviously that's very hand-wavy and not how I'd differentiate.

Think: SaaS application that solves some domain specific problem in corporate accounting, versus "in-browser speadsheet", or "first-person shooter video game with AI, multi-player support, editable levels, networking and high-resolution 3D graphics" vs "flappy bird clone".

When you're working on a product of this size, you're probably solving problems like the ones cited by simonw multiple times a week, if not daily.