Today, Yahoo is giving developers and end users an online "sneak peek" at BrowserPlus, an emerging cross-platform software platform aimed at expanding the kinds of content that run on Web browsers.

The first demos offered as part of Yahoo's browser functionality expansions include features such as drag-and-drop from the desktop, and easier acquisition of data feeds.

Ultimately, BrowserPlus is targeted at allowing Web sites to deploy applications that will set them apart, a goal that seems to dovetail nicely with Yahoo's own recently articulated strategy of growing its series of Web-based Yahoo "starting points."

For the time being, BrowserPlus can only used on sites owned by Yahoo or its partners. But the "first full public release will make BrowserPlus available for use by third-party developers," according to information posted on the Yahoo Developer Network Web site.

Right now, the platform supports Internet Explorer (IE) 7 and Firefox 2 (or greater) on Windows XP and Vista, and Safari and Firefox 2 (or greater) on Intel-based Max OS X Tiger and Leopard systems. But Yahoo also plans to extend BrowserPlus to make it "run in more places," according to an FAQ on the developer site.

"The most unique attribute of BrowserPlus is its ability to update and add new services on the fly without a browser restart or even reloading the page!" contends the BrowserPlus Team in a blog post this morning. "For users, this mans no more interruptions or installers to run. We handle the complexity of software distribution and updates.

"For developers, it means you can check for and activate new services with a single function call (pending user approval, of course)," the post continues.

During the current sneak peek period, registered Yahoo users outfitted with supported browsers can explore demos such as a Flickr photo uploader, a browser-based IRC (chat) client, and a developer tool for exploring Web services output.

Meanwhile, Yahoo is also offering to developers test code samples, along with APIs for initially supported services.

The initially supported services include DragAndDrop, IRC Client, Log, Notify, FlickrUploader, ImageAlter, InactiveServices, PStore, Notify, JSONRequest, and RubyInterpreter. Developers will use a small JavaScript library to deploy these features to users equipped with browsers and downloaded BrowserPlus software.

Yahoo will be eliciting feedback and ideas from developers about services and other issues.

Also according to the BrowserPlus Team, BrowserPlus is headed in an "incrementally" open source direction.

"The main reason we're offering BrowserPlus to external developers, and why we're offering this preview today, is because we're committed to building an open platform that benefits the developer community. We will never charge developers for the use of the platform, and will to continue to incrementally open the platform for developers to use and extend," according to the FAQ.