I spent this weekend at Yahoo's open Hack Day and it was an incredible event. Inspired by past internal hack days, the folks at the Yahoo Developer Network decided to hold an event open to the public. For most of the day Friday, developers from around the world (literally) were given a tour of Yahoo's various APIs (Maps, Flickr, Messanger, Upcoming, mail) by the technical folks behind the various services. They were then set loose on the APIs, powered by candy, pizza and beer. They had until 3:00 p.m. on Saturday to come up with their best stuff, at which time all the teams present their hacks to the judges.

Truth be told, folks didn't actually get right down to hacking after the Yahoo tutorials. First they hung out and chatted with their fellow hackers. Then they pitched tents and drank beer. And then they danced and cheered to an incredible concert by Beck and his band. It was truly an inspired concert. Beck played an hour and a half set, backed by puppeteers with puppets that looked just like Beck and band. The puppets (alright, I suppose it was the puppeteers) even made this great video poking fun at Yahoo. It set the tone for the event. Yahoo pulled out all the stops.

I had the pleasure of being one of the judges for the event. I joined some incredible folks on the judging panel, including Dave Filo, Jeff Weiner, Ash Patel, Bradley Horowitz and Chad Dickerson from Yahoo, Gina Tapani from the fabulous Lifehacker blog, Peter Fenton from Benchmark Capital (upstairs from me), and serial entrepreneur Salim Ismail. Mike Arrington served as master of ceremonies. It took a fair bit of time to run through the 50 or so hacks that were coded overnight but it was worth it. There were lots of fun and interesting ways in which folks were able to put the Yahoo APIs to use.

Perhaps most interesting to me was the fact that a number of companies sent teams of engineers to Yahoo Hack Day to mash up their own applications with Yahoo's services. There were a couple of teams from Plaxo who integrated the Plaxo database into applications like "friends" on Flickr and Messenger. The guys from Technorati built a Yahoo widget to display real time blog discussions. A couple engineers from Mozes, an SMS gateway, built SMS applications on top of the Yahoo web services. The SmugMug team, used Yahoo's UI services to build photo collages. And the engineers from Sharp, who sponsored the event, hacked together their own digital copier to scan documents/photos and automatically post them to Flickr using a the UI on the copier itself. There were also folks from Ruby Red Labs showing off their design chops (and perhaps grabbing some of the extra Hack Day t-shirts for Valleyschwag).

The fact that Yahoo embraced engineers from startups and design shops throughout the ecosystem is indicative of the sort of coopetition that is going on around the web these days. Big organizations like Yahoo, Google and Amazon are making significant pieces of their infrastructure available to third parties for development of new applications. As a result, those big organizations are able to inject their DNA broadly into applications throughout the web. And, by and large, both parties are benefitted by the relationship. Amazon did a brilliant job of extending its reach by allowing the liberal use of its product and review data. Yahoo is now embracing the same philosophy and bringing significant corporate resources to bare on the challenge — case in point, the Yahoo Developer Network and fantastic events like Hack Day. I think it is a really smart move for Yahoo and I suspect we'll be seeing a lot more of it, not just from Yahoo, but from all of its major web competitors, in the months and years to come.