Atlas - 280 North
http://280atlas.com/

Screw Flex, AIR, and Flash for RIAs - we've got browsers, Cappucino and Atlas

280Atlas is a basically Interface Builder written for the browser.

HTML 5 is shaping up to be quite an impressive step up from the capabilities web developers are currently constrained to. One of my favorite new features provided by the spec is support for native drag and drop.

Mockingbird is an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application.

The guys from 280 Slides bring us Atlas based upon their Cappuccino framework.