Ably LiveSync is a potential alternative to MongoDB Atlas Device Sync, offering real-time synchronization of database changes to devices at scale. It allows for large numbers of changes to be propagated to end-user devices in real-time and stores the changes in various local storage options. The solution explores why on-device storage is critical, existing solutions, and demonstrates how Ably LiveSync's MongoDB connector can help with a code tutorial. On-device storage is crucial for apps requiring offline access or fast performance, such as e-commerce inventory apps. It provides several benefits, including offline access, improved performance, cost efficiency, and user experience. Modern mobile operating systems offer various ways to store information on devices, includingUserDefaults, CoreData, SQLite, shared preferences, Room database, and file storage. Ably LiveSync can synchronize data from managed or on-premises databases to mobile devices in real-time, supporting MongoDB and PostgresSQL, with plans to add support for other database engines. The solution involves creating a simple in-store management app using React Native and SQLite for local storage, integrating the Ably SDK callback methods to store documents and changes inside the local SQLite database. It sets up an integration rule that syncs the MongoDB database with Ably, receives database changes from the configured Ably channel, and persists changes locally, ensuring an up-to-date inventory system even when offline. The solution is built on top of Ably Pub/Sub, offering predictable performance, guaranteed ordering and delivery, fault-tolerant infrastructure, high scalability and availability, optimized build times and costs, and a battle-tested deployment process.