The social networking wars got a lot more interesting this week, as Google and a slew of partners -- including still-market-leading MySpace.com -- debuted new APIs to enable the creation of Web-based social applications.

Earlier this year, Facebook launched its own APIs, kick-starting a developer frenzy that helped the site become the Web's go-to spot for social networking. Just last week, Facebook announced an ad and equity deal with Microsoft – reportedly spurning a competitive offer from Google – that valued the company at more than $15 billion. Coincidentally, Google provides ads for MySpace, making the API partnership a natural extension.

Google’s counter-attack, now public in the form of its new OpenSocial APIs, has been rumored for some time. But the reality even surpasses the rumors, with the search giant not only releasing code for cross-site social networking apps but also signing on a slew of partners, capped off by the inclusion of MySpace late Thursday. Other sites announcing they will use the OpenSocial APIs to build social networking applications include Engage.com, Friendster, hi5, Hyves, imeem, LinkedIn, MySpace, Ning, Oracle, orkut, Plaxo, Salesforce.com, Six Apart, Tianji, Viadeo, and XING.

Missing from that list is not only Facebook and its new partner Microsoft but also Web portal Yahoo, which wants in on the social networking game but seemingly lacks a dance partner.

OpenSocial API code is available now at the new OpenSocial Web site. Google’s approach with the new APIs is to tie it to its Google Gadget technology on the client side, which relies on Web-friendly Javascript to build user-interfaces that can be built into Web pages. Google Gears, which lets Web applications store data locally for off-line use, also plays into the client side of the equation. On the server side, the driver is Google’s GData approach for building REST-based APIs utilizing the Web standard AtomPub with extensions for Google data schemas.

Overall, the idea behind OpenSocial is to let developers build applications that can run on any social network – really, any Web site – while being able to take advantage of core user profile data including specific APIs targeting user profiles, activities and persistence.

The “magic sauce” is that not only will OpenSocial apps be able to run on any site that supports the APIs but – at least theoretically – they should also be able to pull in, process and share user profile data from the various sites, essentially creating a platform for Web-wide social “mashups.” How the APIs and especially the “container” Web sites manage user opt-in to sharing their profiles via OpenSocial remains to be seen – and could be a point of contention moving forward.
"You can see how powerful this Web-based model is when you can take the data and knowledge of friends and people and their activities and combine it with a new social networking application platform," said Google CEO Eric Schmidt in a news conference announcing OpenSocial. "We always knew that the Web would be significantly social, we always knew it would have a social framework, and we always knew it would be standard, open and accessible."

On that same press call, MySpace CEO Chris DeWolfe called OpenSocial “the de facto standard for developers right out of the gate. It will have access to 200 million users, making it way bigger than any other platform out there.”

MySpace recently announced it would be building its own developer platform – similar to Facebook’s – to enable third-party app development on its site. That platform will now be based on OpenSocial APIs, DeWolfe said, ensuring that developers won’t have to build multiple versions of their applications to run on different Web sites.

By making OpenSocial cross-site, Google and friends have harnessed their collective capabilities and traffic to counter Facebook. However, because OpenSocial isn’t a site or product in and of itself, it remains to be seen if Web users will opt for the disaggregated, syndicated style of social networking of OpenSocial or prefer to visit Facebook as a destination in which they can interact with friends and colleagues.

Wrote Web 2.0 startup blogger Mike Arrington on his TechCrunch site: “Suddenly, within just the last couple of days, the entire social networking world has announced that they are ganging up to take on Facebook, and Google is their quarterback in the big game.”