If there's any one closed source application I know I depend on, it's Outlook.  And if there's any one open source application that can unseat Outlook, it's Thunderbird -- er, Mozilla Messaging.  Not because it's better than Outlook -- it's not.  Not yet, anyway.

Let's start with the obvious stuff.  I use Outlook daily (as do a great many other people), and a good deal of my work habits center around it -- not just for mail, but scheduling, calendaring, to-do lists, contact management, etc.  I've stuck with it despite its quirks, despite its cost, despite the fact that it's a proprietary, closed source application.  Now I'm considering a switch away, and it sounds like what awaits me in the third edition of Thunderbird may have it.  I tried before, but Thunderbird just didn't have enough of the features I actually needed.

Part of why I'm hoping the next version of Thunderbird does the trick is because of what we could call the Firefox Phenomenon.  Firefox is one of the most hugely successful of open source projects because it's being broadly adopted by ordinary users -- not "experts", but just plain folks.  They wanted, and needed, a better way to browse the Web, and once Firefox showed up they started telling their friends about it.  The results speak for themselves: Firefox is now an unignorable force in the browser world.

The same kind of big-crowd attraction to Thunderbird, if pulled off right, could unseat Outlook among not just the regular masses but corporate users, too.  Existing open source messaging solutions like Zimbra may be great products, but let's face it -- they don't have the same kind of street-level, grassroots cachet that Firefox does.

But a name brand isn't enough to do it -- Thunderbird actually has to be better than Outlook.  Not just free, but worth the investment of time and effort it would take an existing Outlook user to switch to it, to retrain himself to use it, and to get the most out of it. 

That's a tall order to fill. Hardly impossible, though.  But it's just the kind of challenge I like to see taken up by an open source project.