Well it tends to be kind of personal, until you have enterprise contracts and vendor lock-in, and it only needs to be personal to one person with decision makin

Well it tends to be kind of personal, until you have enterprise contracts and vendor lock-in, and it only needs to be personal to one person with decision making power and suddenly you convert a whole company to a product. So you can build a SAAS TODO app and have one killer feature thats useful for 1-1000 or 10,000 paying customers, and survive on monthly subscriptions if you manage to keep churn low. And this can happen in a niche segment or generally just survive off of a few evangelists buying licenses for their company to use X tool. TODO apps are probably never going to be a $billion app but can reach a few million in valuation. But with an ocean of customers and competition, many competing apps can survive and meet a niche. For example we used X small startup app for a few years until we needed Y companies feature, so we moved to Y company instead and it was fairly painless of a transition for <100 users and our simple project/task management requirements.