jStorage is a cross-browser key-value store database to store data locally in the browser - jStorage supports all major browsers, both in desktop and in mobile.
jStorage supports storing Strings, Numbers, JavaScript objects, Arrays and even native XML nodes. jStorage also supports setting TTL values for auto expiring stored keys and - best of all - notifying other tabs/windows when a key has been changed or publishing/subscribing to events from the same or another tab/window, which makes jStorage also a local PubSub platform for web applications.
jStorage is pretty small, about 7kB when minified and 4kB gzipped.