My vote goes to a pair of students at Drew University. Erik Larsson and Del Sockel. In 3 weeks they managed to create a Web based helpdesk tracking and asset management software based completely upon open-source/freeware materials. MySQL, PHP, PERL, and JavaScript being the base of the work, and this is without any prior experience with PHP or MySQL.

And now they're rewriting it with mod_perl to be an apache module content handler that can do it all much faster and more reliably. Sorry to ramble, but I tend to think it's impressive.

--John