BigIdeasDB works backwards from complaints. It analyses more than a million of them, pulled from Reddit, G2, Capterra and the app stores, and turns recurring ones into product ideas with revenue estimates and a build guide attached.
Starting from what people already complain about is a sounder footing than a trend list, because a complaint is evidence somebody hit a problem hard enough to write about it. Pulling from review sites as well as Reddit also catches the grievances of people already paying for software, which are a different and often better class of problem.
It is paid with no free tier. Two things to keep in mind: a well-evidenced complaint still is not proof anyone will pay to fix it, and the revenue figures are modelled rather than observed.
