Today Google is hosting a developer day to show off Google Gears. This new open source browser plugin allows developers like us to build offline web applications using JavaScript APIs. Why is this so cool? Well, it turns out that it is hard to build applications that work offline and online across multiple browsers ~ Google Gears should make it easier.

Nick Gonzalez has reported that the first demo of Gears will be for Google Reader, but assures us more Google applications are soon to come. He explains,

Reader will add a green download button to the user interface. When you click the button, Reader will download the last 2,000 messages to your computer, preparing your computer to work offline or under a spotty internet connection. Downloading will take place in the background, using the asynchronous JavaScript API. While offline you can read these articles and carry out your usual sharing and tagging. When you get back online, just click the button and Reader will sync your offline activity with their server. Right now the syncing is initiated manually, but it's easy to see that it will become more seamless as the program develops. Gears could conceivably solve the large data overhead problems of Google's AJAX applications, pushing updates to your desktop instead of slowing down your browser.

The real news is that the company is releasing the tools using an open source license. It got our attention, and I suspect the attention of thousands of other developers. Smart, very smart.