Currently running on Windows Mobile as an ActiveX control. Just launched Picasa Web Album for Mobile with Gears. Works in IE 6 & 7, IE Mobile 5 & 6, Firefox 1 & 2 (3 coming soon). Firefox plugin works on Mac. Safari support being worked on. The Mobile version has the same API as the desktop version. Google have also announced that they are porting Gears to Android (no surprise there…) — this will be a Netscape standard plugin, so will probably come to WebKit at a similar time.
Gears is a browser plugin that provides additional APIs to the browser (local storage in a SQLite database, worker threads, local server for server data offline). See http://code.google.com/apis/gears/ for documentation and samples.
Mobile version also provides a Desktop API, which allows creating an icon shortcut to the app. Can provide multiple resolution icons.
Worker threads cannot access the DOM and the
window object, so Gears also provides HttpRequest and Timer APIs for them.
Security: Gears will ask the user if a URL wants to store and access information locally. Thereafter that URL is allowed to use Gears to access data from the same origin (scheme, host, port).