From the game's Kickstarter launch:
Storium is a web-based online game that you play with friends. It works by turning writing into a multiplayer game. With just your computer, tablet, or smartphone, you can choose from a library of imaginary worlds to play in, or build your own. You create your story’s characters and decide what happens to them. You can tell any kind of story with Storium. The only limit is your imagination.
Storium uses familiar game concepts inspired by card games, role-playing games, video games, and more. In each Storium game, one player is the narrator, and everyone else takes on the role of a character in the story. The narrator creates dramatic challenges for the other players to overcome. In doing so, they move the story forward in a new direction. Everyone gets their turn at telling the story.
This listing is for the game system employed by Storium.com