The other day I posted a blog about disruption and I used a screenshot from Visicalc with a link to Dan Bricklin's site. Dan, along with Bob Frankston, was the co-creator of VisiCalc, the first electronic spreadsheet. These days, Dan has focused on open source software and has now developed wikiCalc, an open source wiki-spreadsheet. It's written in Perl and available under the GPL through his company Software Garden. It's also being released under a commercial license by SocialText under the name SocialCalc. I don't know that wikiCalc is disruptive the way that VisiCalc was 25 years ago, but its a darn good piece of software.
On the other hand, maybe there's something more important to wikiCalc than the fact that its an opensource, web-based spreadsheet. There may be some irony in the fact that that both Windows Vista and wikiCalc shipped more or less in the same week. At this point, most computer users are pretty unmoved by changes in Windows or in desktop applications. I can't recall any significant changes to Microsoft Office in the last ten years, but maybe that's just me. (Ok, it was great when they executed Clippy, but otherwise, fugeddaboutit.)
Perhaps the real significance of wikiCalc is that it can serve as a platform for web-based application-specific spreadsheets that can be integrated into other applications. For example, wikiCalc could integrate in with hosted CRM applications, reporting tools, ERP systems and so on. Why not use the full power of a spreadsheet whenever its needed?