Customer outcomes · Consumer product · our own, on both app stores
Relay Tracker: an offline-first race coordination app, end to end
Our own product, shipped to Google Play and the App Store. Works fully offline, predicts every leg, and syncs three ways.
- Android
- iOS
- Spectator web
- Offline-first
Live leg and plan screensrelay-tracker.com
The situation
Two vans, overnight, no cell signal
Overnight, multi-leg road relays are run by two vans of sleep-deprived people trying to be at the right exchange point at the right time, usually with a spreadsheet, a group chat, and no cell signal.
- Estimates drift as the race goes on.
- Nobody knows where the runner is, and the van leaves late.
- A spreadsheet and a group chat hold it together, until the signal drops.
What we built
A pace model on the phone, and three ways to sync
A mobile app for Android and iOS that works fully offline, with a spectator site and a training-plan builder that share its engine.
- On-device pace model. Runners' recent times, distance scaling, hill cost, fatigue across legs and heat give earliest, expected and latest arrival for every leg; it corrects itself from real splits.
- Three sync tiers on an append-only event log, so nothing conflicts: cloud when there is signal, phone-to-phone at van exchanges, a QR code as the last resort.
- Spectator site for friends and family, and a plan builder whose JavaScript engine is a line-for-line port of the app's model, guarded by a parity test with over 12,000 assertions.
- Seasons and team records survive yearly rollovers; estimated splits are never counted as records.
Results
Shipped, tested, used live
Shipped through continuous delivery and used live at a 2026 overnight relay, where an arrival-time drift was diagnosed and fixed during the race.
- Platforms
- Android · iOS · web
- Automated tests
- 1,389plus a 12,000-assertion app/site parity test
- Sync paths
- 3cloud, phone-to-phone, QR
- Works offline
- Yesdesigned for cell dead zones
relay-tracker.com Google Play App Store
Measured or customer-reported. Every number on this page is one or the other; anything unmeasured says so.
What it looks like
Three more screens
