Each one exists because of a specific complaint about an app that already existed. All free, all small enough to install on a metered connection, all working without an account.
A Pomodoro timer that keeps counting when the screen goes off.
Built against: Timers that stop counting when Android reclaims the process, losing the session.
One arithmetic ladder a day. Five problems, one attempt, the same for everyone.
Built against: Brain-training apps cap free play at about three games a day, on top of cognitive claims the evidence does not support.
Your whole Spotify listening history, read from your own data export, in the browser.
Built against: Listening stats built on Spotify's API, which reports that a track played but never for how long, and holds only the last fifty plays.