It’s kind of like Quicksilver or LaunchBar, but in a bookmarklet for your browser. A system of commands lets you quickly search the page or various services, start a post in MarsEdit and link the current page, share the page on sites like Delicious, Twitter, and Facebook, perform HTML5 validation, clip a page to Evernote or LittleSnapper, subscribe to a site’s feed in Google Reader, and a ton more.
The goal is to provide a lot of the functionality of plugins that can often bog down a browser, but in a browser-agnostic and performance-friendly bookmarklet. Less glam and pretty buttons, but more speed and a surprising amount of flexibility. It even works on the iPhone.