[cellarius]

It takes you to a social sharing/discussion platform. Normally as you say it would be external. But many sites offer their own discussion platforms, normally forums. It would greatly benefit those sites if next to the well known external providers there would be a universally known icon for discussion forums that could be put next to those sharing icons. Insofar it does indeed compete with FB, Twitter and the like, as it makes your forum more visible at the place people who like to comment on something tend to look.