Google+ Sign-In, if your site uses it. The recommendations will show up regardless of if the reader is signed in to Google, but if they are, the recommendations will also show if anyone in their Circles have +1-ed other articles.The new feature will appear on mobile optimized versions of websites, and Forbes is the first partner. The recommendations will slide up from the bottom of the screen and will show other articles on your site that have been +1-ed by others on Google+ or content that is popular with those who use
The recommendations sound pretty easy to implement, and will show up on all iOS or Android devices. No word yet on any other content partners, but given how easy it is to implement, don't be surprised if it shows up more and more.