There are several reasons that Yahoo! released some of their core UI code for free. A callous read of this would suggest that they did it to steal back some goodwill from Google (still riding the successful Goolge API release from 2002). A more charitable soul could suggest that Yahoo! is interested in making the web a better place, not just in their market-share. Two things suggest this—the code is available under an open BSD license, and their release of design patterns. The code is for playing with; the design patterns for learning from.
The code is squarely aimed at folks like me who would struggle mightily to put together a default library to handle complex interactions in Javascript using AJAX (all the rage now) while dealing with the intricacies of modern and legacy browsers. Sure, I could pull together the code from different sources, test it, tweak it, break it, tweak it some more, etc. Unsurprisingly, I’ve never gotten around to it. The Yahoo! code release will literally save me at least a hundred hours. Now I can get right down to designing the interaction, rather than dealing with technology.
The design patterns library is a collection of best practice instructions for dealing with common web UI problems, providing both a solution and a rationale, with a detailed explanation of the interaction/interface feedback. This is something that is more familiar to me, but still stands as a valuable resource. It is a well-documented alternate viewpoint and reminder from a site that serves more users in one day than I’m likely to serve in a year.
Of course Yahoo! is hoping to reclaim some mind-space from Google with developer community goodwill. But since the code is general release, and not brandable in any particular way (it’s all under-the-hood kind of stuff), it’s a little difficult to see the release as a directly marketable item. It really just seems like a gift to the network, and hopefully one that will bear lovely fruit. It’s always heartening to see large corporations opening their products to the public as a way to grease the wheels of innovation.