I really liked the idea of Google+ circles. Creating "containerized" groups of people (things?) that I could act on in a complete unique way was really cool. I could say something in my "friends" circle that I couldn't (or would be misunderstood) in my "family" circle. I could also keep track of technology (Linux, Tesla, etc.) in another, completely separate, area.

I wish that a "social" network would bring back the idea of Circles.