Why and when did OpenStreetMap introduce 'Add Friends' feature?

Currently, I am doing a research on ‘Investigating and Improving the involvement of Digital Volunteers in OpenStreetMap movement’. I am curious to know why and when did OpenStreetMap introduce ‘Add Friends’ feature in OSM.

Look at this:

So it was in 2007 probably. Pretty much at the beginnings of OSM as we know it, I guess.