Gmail's desktop offline mode relies on browser extensions, but Google engineers have figured out a way to use HTML5 standards—supported by the iPhone, Android and Pre's webkit browsers—to accomplish the same thing natively.

Google demonstrated a new Gmail mobile web app that leverages the HTML5 database and app cache features, which allow web apps to store certain types of data locally, much like Google Gears. The result is a super-slick app that retains a database of messages even when your cellphone lack any connectivity, and that'll allow regulars tasks—message composition, deletion, and organization—to be queued up for synchronization when the phone next has service.

Offline email in itself isn't a revelation, but the fact that this app—and other conceivable apps that could effectively leverage the same technology—could work on any phone with WebKit-based browser is fantastic. That includes, for now, the iPhone, any Android phone, the Pre and some S60 phones. Where complex web apps kind of sputtered in lieu of native applications on the iPhone, the potential reach of rich, pan-platform WebKit applications could be enough to spur some really exciting stuff. [iPhoneBuzz via Mobilecrunch]