Bubbl.us doesn't offer much beyond collaborative flowcharting, but does that well.
|(click for image gallery)|
Unlike other tools listed here, Yugma isn't wholly a Web-based product; there's a download that must be installed on the presenter's machine to run things. If people want to participate in the presentation in a viewing-only mode, they just need a Web browser with Java. Control over the meeting (including control over shared desktop apps) can also be delegated to others during the session, provided they have the software on their end.
People can also dial in by conventional phone and share in the conference by voice. For those on Skype, there's a Yugma add-on for that well-known Internet phone application that lets you invite existing Skype users into a Yugma session.
Yet another goofily named site that's actually quite useful, Bubbl.us allows users to collaboratively create "mind maps" or organizational flowcharts. It's sort of like a stripped-down version of DabbleBoard, since its tools specifically center around mind maps, but the level of control and detail you have over the objects in the maps you create is impressive.
You don't need to create an account with Bubbl.us to start making mind maps, but you'll have that many more options at your command if you do (sharing, etc.). The behavior of the mind-map editor is a little quirky at first, but you quickly get used to it -- you grab and drag anywhere blank to scroll around the map, and hover over existing objects to expose their control handles and editing options. The finished sheet can be exported as HTML or XML.
A 2.0 version of Bubbl.us is under wraps but still quite usable. From what can be seen so far, it sports an Office ribbon-like interface and a slightly cleaner presentation, although the basic toolset is the same. Future projected features include real-time collaboration and site-wide search for saved sheets.
InformationWeek Analytics has published an independent analysis of the next-generation Web applications. Download the report here (registration required).