Yahoo is holding <A HREF="http://www.eweek.com/article2/0,1895,2016665,00.asp?kc=EWWSUEMNL092006EOAD">its first public "Hack Day"</A> at the end of September for developers to spend 24 hours building applications around Yahoo's APIs. On Sept. 29-30, Yahoo will open up its Sunnyvale campus to 500 developers for a free all-day developer workshop, followed by what the company calls a 24-hour "hack-through-the-night" festival that will include an outdoor party.