Couchbase Lite : Lightweight NoSQL Database for iOS and Android
Couchbase Lite is a lightweight, embedded and syncable NoSQL database engine. It is a reliable, secure JSON database that is built for online/offline mobile application needs. Couchbase Lite compiles natively for iOS and Android. Couchbase Lite stores records in flexible JSON format and records/documents can have arbitrary-sized binary attachments, like multimedia content. It uses map/reduce indexing that allows for fast lookups without needing to use special query languages.
The database engine is a library linked into the app, not a separate server process and at under 600kb, it has a very small code size. It has a very fast startup time and low memory usage. Couchbase Lite is also syncable which means that any two copies of a database can be brought into sync using a REST-based protocol.