The service, currently available for Mac OS X clients, with a Windows version planned to debut soon, scans your iTunes library for installed applications, presents them on the Web in a faux iPhone interface, and encourages you to share your library with friends by way of social networks, including Twitter and Facebook.
The purpose? Helping solve the discovery of relevant applications - a process Ouriel says is "ignoring".
The service is in closed alpha now, but we have 50 invites available, first come, first serve to Mac OS X users. http://bit.ly/appsfireLG
You can see some example Appsfire libraries here:
Also part of Appsfire? A new link shortener for iPhone developers and bloggers, who all know the usual links to the iTunes Store are a complete pain. You can find that here.
An intro to the service can also be found on YouTube.