Developer builds offline-first Rust sync engine using event sourcing for mobile apps

A developer has open-sourced a custom offline-first sync engine called rust-mobile-offline-sync, built for TrainVision, a mobile platform designed to collect machine-learning training data in low-connectivity environments. The core logic is written in Rust and shared across iOS, Android, and a Rust backend using UniFFI-generated Swift and Kotlin bindings, with SQLite on-device and Postgres on the server. After evaluating existing solutions like Couchbase Lite and ObjectBox, the developer found them too restrictive for custom conflict resolution and chose to build a bespoke engine instead. The solution centres on event sourcing, where devices store an append-only log of domain events rather than mutable state, making sync a matter of exchanging unseen events rather than comparing full entity snapshots. This approach makes sync operations naturally idempotent and eliminates the guesswork typically involved in merging conflicting offline edits.