Ask HN: Twitter/tumblr/etc “in a box” platform?

Hey HN- I am looking at building a service semi similar to a twitter/instagram/tumblr which basically involves people following other people to see their content and vice versa. For the sake of argument, imagine I wanted to build a twitter clone that was purely for cat pictures.

Is there a open source system out there which has most of the scaling/distribution issues solved for that type of setup? Im loathe to write my own follower/following system out of fear of the scaling issue.

Language agnostic but would prefer PHP or Node