CouchDB

Apache CouchDB stores each record as a JSON document and exposes it over a plain REST interface, so any HTTP client can read and write without a special driver. Changes flow out through a continuous append-only log, which makes bi-directional multi-master replication between sites and offline-tolerant mobile sync straightforward to set up.

It suits content and catalogue services, configuration stores, and collaborative tools where document shapes drift over time and revision history matters.

Running it yourself keeps the JSON and its history on infrastructure you control, with replication and snapshot handling done by tools you already operate.