Opera Unite is an extensible framework that allows for several web services (referred to as...
Opera Unite is an extensible framework that allows for several web services (referred to as "Applications") to be hosted from the user's computer, including a web server for hosting a site, file and photo sharing, a chat room, and streaming media. Opera Software has released an API to create new or improved applications for the Opera Unite Platform, and many have already done so. An Opera Unite user's applications run on a domain associated with their My Opera Community account, and are accessible from any web browser. For these applications to be accessed, the computer and the Opera Browser hosting the applications must both be running.
Will be removed with Opera 12.
Opera plans to remove it from the browser along with the widgets since they would like to focus their efforts on extensions. Sad but apparently true: http://my.opera.com/addons/blog/2012/04/24/sunsetting-unite-and-widgets