CouchDB : Apache CouchDB™ is a database
that uses JSON for documents,
JavaScript for MapReduce indexes,
and regular HTTP for its API
Kinto : Kinto is a lightweight JSON storage service with synchronisation and sharing abilities.
LokiJS : A fast, in-memory document-oriented datastore for node.js, browser and cordova
DOM Storage Query Language : DOM Storage Query Language (DomSQL) is an SQL inspired interface for DOM Storage (or Web Storage as defined in the W3C working draft).
A Lawnchair is sorta like a couch except smaller and outside. Perfect for HTML5 mobile apps that need a lightweight, adaptive, simple and elegant persistence solution.