Upworthy is a website for viral content started in March 2012 by Eli Pariser, the former executive director of MoveOn, and Peter Koechley, the former managing editor of The Onion. One of Facebook's co-founders, Chris Hughes, was an early investor.
Upworthy's stated mission is to host the intersection of the "awesome", the "meaningful" and the "visual." It uses virality to promote stories with a liberal bent on social issues. 
In June 2013, an article in Fast Company called Upworthy "the fastest growing media site of all time".
They popularized a certain style of headline, particularly a style of two-phrase headline which is very recognizable, which has spread to many other websites. Examples of such Upworthy style headlines:
"We Don’t Hear Enough From Native American Voices. Here’s An Inspiring Message From One."
"Someone Gave Some Kids Some Scissors. Here’s What Happened Next."