From the author,

“Starting with Safari 4, iPhone/iPad OS3, Chrome 5, and Opera 10.5 (Desktop), HTML5 Local Databases are now supported. I’ve been reading about local databases for quite some time  and decided to do a write up with some basic examples on how to get started”

Getting Started with HTML5 Local Databases

Ben Lister

From the HTML5 spec,

“This specification introduces a set of APIs to manipulate client-side databases using SQL.”

HTML5 Database

Remy Sharp