At this point, it's not too surprising when Internet companies release the code to certain products to independent developers in order to foster greater innovation with their products. However, Yahoo! (NASDAQ:YHOO) may surprise a lot of people by revealing the code of one of its most popular products, Yahoo! Mail.

Over the course of this summer, there's been a rash of such behavior, with the idea that an open-source outlook can help products gain traction in many interesting and innovative applications that the companies themselves might not even think of. That's the beauty of the mashup culture, even though it might end up producing some strange bedfellows, as users meld together the programs they love across the Web. (Some good examples of mashups include Yahoo! Maps paired up with Craigslist to show apartment listings, for example, or Google's (NASDAQ:GOOG) own mashup of its Google Maps product with environmental summer vacation hot spots.)

Last spring, both Time Warner's (NYSE:TWX) AOL and Yahoo! opened up their IM clients to independent developers to foster their use in new and different ways -- which might have seemed an odd move, for AOL anyway, since AIM has been a rather closely guarded application because of its popularity and leadership position.

Yahoo!'s move with Yahoo! Mail strikes me as similarly surprising, since Yahoo! Mail is very highly trafficked and, as such, is one of Yahoo!'s most important assets. I can't help but think of one piece of news from July -- when Yahoo! Mail was knocked out of Hitwise's No. 1 spot by News Corp.'s (NYSE:NWS) MySpace. Granted, Hitwise tracks total visits, not unique visitors, when it's tracking Internet market share, but it's still an interesting data point. In August, the same trends continued, according to Hitwise, with Yahoo! Mail in the No. 2 spot, trailing MySpace, while took the No. 5 position in the top ranking. (Yahoo!'s main page came in at No. 3, Google's main search page was No. 4, and Microsoft's Hotmail came in at No. 5, in case you're wondering how the popular sites stack up.)

Of course, the fact that leaders may open up their products may be surprising, but it's certainly not illogical. With the amount of competition right now, it bodes well that they shouldn't lose their competitive advantages by not moving with the times -- namely, by not giving Internet users what they want. And clever applications using their products should certainly help them. The sky's the limit when it comes to mashing up different products and services. A Reuters article pointed out that one enterprising young developer mused on the idea of a mashup between Yahoo! Mail and Yahoo!'s Flickr user-driven photo service offering visual clues as to email's content.

It should be interesting to see how the influence of independent developers on products that we're all well accustomed to sparks the creative evolution of those products, and how much the companies will benefit from such open relationships with their products.

For more mashup madness, see the following articles:

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Alyce Lomax does not own shares of any of the companies mentioned. The Fool has a disclosure policy.