I built an app that charges you real money when you miss your goals
Beeminder for tasks that charges you immediately when you miss a deadline.

Permissionless enforcement + charity splits make cheating expensive, but it's a blog post about one person's experiment.
Individual experimenter / fitness enthusiasts willing to experiment with financial commitment mechanisms
Beeminder for tasks that charges you immediately when you miss a deadline.
It refuses the modern fitness app script: no accounts, no servers, truly offline and a CSV export so your logs live with you. The UI is spare and fast — instant set logging and basic progress charts — but it doesn't push past the basics (no wearable sync, advanced analytics, or social features), which is fine if you just want a distraction-free training journal.
Systematically diffs locales to find missing strings when LLMs skip them.
Fitness + territory conquest is a fun concept, but Ingress/Pokémon GO already nailed this.
100GB JSON files open on Android with Rust + SIMD when every other viewer crashes.
Zwift alternative running entirely in the browser with no app install required.