It's called the "Send To" option. This somewhat clunky name comes as a result of TOR already having an option for sharing via a unique RSS feed, but in spite of the clunky name this new feature is still incredibly useful and offers broad support for many different platforms.
In addition to the three default sharing options, users can also go into the settings menu and enable sharing buttons for Tumblr, Google+, Buffer, Evernote, and more. And if The Old Reader neglected to include the social network of your choice, there's even a way for users to define their own sharing option.
And best of all, users get to share the source link and not some shortened and redirected link (like bitly). Given the brouhaha over the weekend concerning Feedly I know that at last a couple readers will be pleased. I myself am indifferent to how the link goes to the content, just so long as I can share a link to the original content.
The Old Reader is neither the largest nor smallest of the news reader services that have thrived after the Readerpocalypse, but it does boast a fiercely loyal user base. It had over 400,000 users in late July, which was shortly before the service was sold.
This service launched in May 2012. I'm told that it was originally intended to capture and maintain certain features of Google Reader, but it is missing others. For example, I can't find an option for a simple black text on a white background. I also can't figure out what happened to the folders full of feeds (they weren't imported, I think), but that could well be a bug.