PB
Problem
Mental arithmetic is a skill almost everyone has let rust, and the apps that promise to fix it are mostly stopwatches with a leaderboard bolted on. They measure how fast you already are, tell you nothing about why you got something wrong, and lean on streaks to drag you back. People quit inside a week, not because the maths is hard, but because the pressure is exhausting and nothing is actually being taught.
Why I built it
I wanted the opposite of a drill app: something closer to a gym. Five to eight minutes a day, no calculator, no timer counting down on screen. Short enough that it survives a real routine, and honest enough that it tells you what you’re actually bad at instead of handing back a score.
What it does
A three-minute placement reads you skill by skill and reports back in words (which track is strong, which skill is holding you back) rather than as one number. Every new skill then arrives with a named technique (make a ten, round and correct) and a worked example, so you learn a method instead of grinding repetitions.
Each day’s session is mixed from three things: your weakest skill, whatever spaced review is due, and one challenge. Levels are tracked per skill, never as a single global figure, so progress stays legible. Sessions cache a week ahead, so a commute or a flight doesn’t break the habit.
The restraint is the feature: one reminder a day, at most three times a week. No streak warnings, no leaderboards, no confetti.
Engineering decisions
Native Swift and SwiftUI, built for iPhone with a bespoke iPad layout rather than a stretched-up phone screen. The learning engine (placement, adaptive difficulty, spaced review, interleaving, and mistake diagnosis) is deterministic and unit-tested, because a trainer that misjudges what you know is worse than no trainer at all. CloudKit handles sharing and sync, WidgetKit surfaces progress at a glance, and the question model is structured for localisation from the start rather than storing finished English sentences.
Current state
In active development. The marketing and support site is live; the app is not yet on the App Store.