AOL on Monday expanded its Open AIM initiative, adding support for PC-to-PC calling and new operating systems including Mac OS X and Linux. The Open AIM program provides a platform for developers to build plug-ins and custom clients that take advantage of AOL's instant messaging network.

Since its launch in March, the Open AIM effort has attracted 35,000 registered developers and over 100,000 consumers using AIM gadgets. Five custom clients have been built using the SDK. "We had a pretty good start and now we're seeing it really get some legs," AIM chief architect Justin Uberti told BetaNews.

The latest update brings to the table location based services that enable users to see where their buddies are located. AOL has released a plug-in for its own AIM Triton client, and foresees developers building mash-ups with maps. The location information is obtained based on a user's IP, but AOL downplayed any privacy risk.

"We're very concerned about privacy. Only people on your buddy list can see the information," Uberti told BetaNews. "We are certainly not tracking any historical location information. The service is meant to show where you are right now, not where you've been."

Developers can now also easily build AIM bots through the Open AIM program. AOL has added sample code and scripting programs that are designed to help turn any AIM screen name into an automated bot. AIM Talk's PC-to-PC calling is additionally available to Open AIM developers, who can now access the APIs using Java as well.

Perhaps most significantly, the Open AIM program has been expanded to operating systems other than Windows. Developers can build AIM-based solutions for Mac OS X, Linux and even Pocket PC. Audio and video functionality is not available on Macs, and AIM's advanced security features cannot be used on Linux, but other functionality is fully supported.

AOL says it has no plans to build a Mac OS X or Linux AIM client of its own on the new platform. The company feels third parties can better serve those operating systems, adding that "we have our own areas of strength."

However, there are some restrictions to the Open AIM licenses. Those who use the APIs to build a custom client cannot connect to multiple IM networks, which means popular software such as Trillian and Adium will not be able to make use of the SDK.

In addition, each license key embedded into a program can only log-in to the AIM network 250,000 times per day, or 2 million times per month, limiting the potential user base. If an application is reaching that level, AOL says developers can approach the company and forge a business partnership.

Looking forward, AOL told BetaNews that Google support would be coming to the Open AIM program when it reaches the main AIM Triton client later this year. As part of an investment deal, Google and AOL agreed to connect their IM networks. Microsoft is testing similar integration with Yahoo's messaging network.

"We continue to work on [Google integration] and it will be supported by the Open AIM initiative in the future," said Uberti.