Offline sync alternatives
MongoDB deprecated Atlas Device Sync in September 2024 and removed it on September 30, 2025. The Realm on-device database continues as an open-source project without sync. The replacements solve different problems. PowerSync syncs your backend database into SQLite on each client. Couchbase Lite is an embedded database that syncs with Couchbase servers and, with its peer-to-peer replicators, directly between devices. Offline Protocol replicates shared documents device to device with no server, and your database stays the system of record. If you need your server data on the device, Offline Protocol is not the replacement.
Covers itPartly, or with conditionsNot part of the product Taken from each product's own documentation. The detailed table below carries the specifics.
The specifics
| Capability | Offline Protocol | Atlas Device Sync | Couchbase Lite | PowerSync |
|---|---|---|---|---|
| Status | In active development; current release v0.30.0 | Deprecated September 2024; removed September 30, 2025 | Active; Couchbase Lite 4.1 | Active |
| What syncs | Replicated documents (map, list, text, counter) between devices | Realm objects between devices and MongoDB Atlas | JSON documents between devices and Couchbase Server or Capella | Rows from your backend database into SQLite on each client |
| Device to device with no server | Yes, over a Bluetooth LE mesh or a relay | No | Yes, with the peer-to-peer replicators over Wi-Fi and, since 4.1, Bluetooth LE | No, client to server |
| Backend | None required; your database stays the system of record | MongoDB Atlas | Sync Gateway or Capella App Services | Postgres, MongoDB, MySQL, or SQL Server, through the PowerSync Service |
| Queries on the device | None; documents are replicated state | Realm queries | SQL++ and a query builder | SQLite |
| Client platforms | iOS and Android through React Native, with early native Swift and Android packages and a preview Flutter plugin; Rust; Python on PyPI; Java on Maven Central; a C API | Realm SDKs; community branches without sync | Android, iOS, .NET, C, and community JavaScript | Web, React Native and Expo, Flutter, Kotlin, Swift, .NET, and more |
| Licensing and cost | Mesh SDK free under AGPL-3.0, including in production. Closed-source and App Store apps need the commercial license; contact us for pricing. Hosted services from $0 (Free), $99 a month (Pro), $499 a month (Scale). Local mesh traffic is never metered. Pricing | Realm database open source under Apache-2.0, without sync. MongoDB notice | Community Edition Apache-2.0; Couchbase Mobile priced on request. Couchbase pricing | Client SDKs Apache-2.0 or MIT, service under the FSL; free, cloud, and self-hosted plans. PowerSync pricing |
How they differ
Atlas Device Sync kept Realm databases on phones in step with MongoDB Atlas. MongoDB deprecated it in September 2024 and removed it on September 30, 2025, and its deprecation notice lists alternatives including Ditto, PowerSync, and ObjectBox. The Realm database itself continues as an open-source project, with community branches that remove sync.
PowerSync replaces the server-to-device half. Its service replicates data from Postgres, MongoDB, MySQL, or SQL Server into SQLite on each client and streams changes as they happen, and client writes go back through your own backend. It has client SDKs for the web, React Native, Flutter, Kotlin, Swift, and more. It does not sync devices with each other directly.
Couchbase Lite is an embedded document database that syncs with Couchbase Server or Capella through Sync Gateway or App Services, with SQL++ queries on the device. Its peer-to-peer replicators sync devices directly over Wi-Fi and, since version 4.1, Bluetooth LE, forming a mesh with TLS between peers. Couchbase lists peer-to-peer sync with its paid Couchbase Mobile offering.
Offline Protocol is not a database. Its replicated documents (maps, lists, text, and counters) are shared state that devices edit offline and merge deterministically when they meet, over a Bluetooth LE mesh or a relay, inside MLS-encrypted groups. Documents persist on the device, the storage underneath is a swappable adapter, and your existing database stays the system of record. It fits field apps where devices must share state with each other while disconnected, and it can run alongside a backend sync tool.
When to choose each
Choose PowerSync if you need your Postgres, MongoDB, MySQL, or SQL Server data on each device as SQLite, synced through a server. Choose Couchbase Lite if you want a full embedded database with queries, server sync, and peer-to-peer replication from one vendor. Choose Offline Protocol if devices must share and merge state directly with each other without a server, encrypted end to end, while your current database stays the system of record.
Choose PowerSync when
Your data lives in Postgres, MongoDB, MySQL, or SQL Server, each device needs its slice of it offline as SQLite, and devices reach your backend often enough to sync through it.
Choose Couchbase Lite when
You want an embedded document database with queries, sync to Couchbase servers, and peer-to-peer replication, and a Couchbase deployment fits your stack.
Choose Offline Protocol when
Devices in the field must share and merge state with each other while disconnected, over Bluetooth LE or a relay, encrypted with MLS, and your existing database stays where it is.
See how replicated documents work, or the CRDT and offline-first entries in the glossary.
Offline sync alternatives FAQ
What replaced Atlas Device Sync?
MongoDB removed Atlas Device Sync on September 30, 2025, and its deprecation notice lists alternatives including Ditto, PowerSync, ObjectBox, AWS AppSync, HiveMQ, Ably, Parse, and Cedalo. Which fits depends on the job: syncing a backend database to devices (PowerSync), an embedded database with server and peer-to-peer sync (Couchbase Lite, Ditto), or shared state between devices with no server (Offline Protocol). Read the MongoDB deprecation notice.
Is Offline Protocol a Realm replacement?
Not for most Realm apps. It has no query language and does not sync your backend database to the device. It replaces the part of Realm sync that kept nearby devices in step: replicated documents that devices edit offline and merge when they meet, over Bluetooth LE or a relay, with no server. It can run alongside a backend sync tool.
Does PowerSync sync devices directly with each other?
No. PowerSync syncs between your backend database and SQLite on each client, through the PowerSync Service. Devices that must share state while offline and out of reach of the server need a peer-to-peer path, such as Couchbase Lite's peer-to-peer replicators or Offline Protocol's replicated documents.
How do licensing and cost compare?
The Offline Protocol mesh SDK is free under AGPL-3.0-only, including in production, and local mesh traffic is never metered on any plan. Closed-source apps and apps distributed through the Apple App Store need the commercial license, which has no published price, so contact us for pricing. Hosted services are optional and run on Free ($0), Pro ($99 a month), Scale ($499 a month), and Enterprise plans. PowerSync's client SDKs are Apache-2.0 or MIT and its service is under the Functional Source License, with free, cloud, and self-hosted plans on its pricing page. Couchbase Lite Community Edition is Apache-2.0, and Couchbase Mobile, which lists peer-to-peer sync, is priced on request. See Offline Protocol pricing.
