Looking for a place to live last year, Paul Rademacher pored over Silicon Valley rentals on craigslist, the popular online classified-ad site. But the 3D-software engineer grew frustrated that he couldn't see the properties' locations on one map. So Rademacher hacked his own solution -- a Web site that combines craigslist rentals with search engine Google Inc.'s (GOOG
) map service. The listings on HousingMaps.com appear as virtual pushpins on maps of nearly three-dozen regions around the country. Click on one, and up pop the details. Since its public debut in April, the free site has drawn well over a half-million unique visitors.
What they're all seeing is nothing less than the future of the World Wide Web. Suddenly, hordes of volunteer programmers are taking it upon themselves to combine and remix the data and services of unrelated, even competing sites. The result: entirely new offerings they call "mash-ups." They're the Web versions of Reese's ("Hey, you got peanut butter on my chocolate!") Peanut Butter Cups.
