Kinto

Kinto is an open source JSON document store that specializes in syncing data between devices and servers. It was originally developed by Mozilla as the backend for Firefox Sync, handling browser settings, bookmarks, and tabs. The service stores data as collections of JSON records, each with automatic timestamps and conflict resolution. It uses a simple REST API with authentication via accounts or tokens.

Kinto runs on Python with PostgreSQL as its primary database, though it also supports other backends. It offers features like permissions per collection, change tracking for sync, and batch operations. The server can be deployed with Docker or from source, and client libraries exist for JavaScript, Python, and other languages. Mozilla still uses it for Firefox Sync, but it works as a general purpose sync server for any application data.

This tool fits best for developers who need a reliable sync layer for user settings or app data without building their own. It is free and open source under the Apache 2.0 license. The project is maintained by the community with Mozilla's backing, and its documentation covers deployment, configuration, and client integration thoroughly.