Every app idea has a boring 90% and a nasty 10%. The boring part is CRUD, auth, a settings page, Stripe. The nasty part is the one subsystem that decides whether the thing works at all, and it’s usually not the part that looks hard in the pitch. Below are nine builds worth attempting, with the nasty 10% named up front so you can decide whether you want to spend your weekends there.

The romantic narrative of the solo developer who builds an app in nights and weekends, publishes it to the App Store, and generates meaningful income from passive sales is not entirely false. It is sufficiently true in enough specific cases to sustain the mythology and sufficiently rare to make the mythology dangerous as a planning assumption.

The structural conditions that made the App Store a viable path to meaningful passive income for individual developers in 2010 to 2015 have changed. The App Store had fewer apps. Discovery was less competitive. Users were more willing to pay upfront for apps they had not tried. The apps that met a basic need in a well-executed way could find their audience without significant marketing investment.