David Ehlers

This looks interesting…

http://developer.yahoo.net/blog/archives/2008/04/introducing_the_1.html

Y!OS platforms will harness Yahoo!’s unique strengths – our rich and relevant user experiences (we’re #1 in 7 verticals), our massive audience (half a billion users/month), and our deep data repositories (content, content, content) – and open them to the innovations of the developer community. Our aim: to fundamentally transform how people experience Yahoo!.

With Y!OS, we’re moving from a model in which each Yahoo! property develops much of its own technology to one where we share common data and frameworks that can be easily surfaced across multiple Yahoo! properties and off the Yahoo.com network.

It’s a major rewiring of Yahoo!.

And the good news for developers is that Y!OS will allow you to access to these assets, build applications around them, and then get distribution on Yahoo!’s monumentally popular properties (and/or use them in your own websites).

includes: 

• A Single Social Platform for Yahoo!
• Lotsa Standardized Web Services
• The Yahoo! Application Platform (YAP)

Not exactly sure if it is the “Top 40 Free Downloadable Open Source Social Networking Software” but worth a mention…link