It's "reddit on a proof of stake blockchain" with what's supposed to be a USD peg called "steem dollars". It was mainly premined by Reverend D. Larimer of Bitshares fame ("dantheman" on Steem). It seems like he made the software totally impossible to use, released it into the wild, mined almost all of it, then opened up the whitepaper and Reddit-clone website to the public.

People click to up vote and KAZAAM, internet funbux appear! It's what we always wanted: a version of Reddit that pays money to people and is not censorable, which could only do wonderful things for r/creepshots.