From the introduction:
Wondrous is a collaborative storytelling game with simple mechanics designed to give minimal resistance to the narrative. For each gaming group, one of the people playing this game will be the gamemaster (GM) who will facilitate the game play by telling the other players about what is happening in the world, controlling the non-player characters (NPC’s), and determining the difficulty and nature of the challenges that the other players characters will face. The other players will be controlling their own player character (PC). While everyone involved is crafting the story together, the GM has the most responsibility because they are in charge of many more aspects of the game, including having the final say in disputes.
Note the copyright on the game document states 2017, though the game was published in 2016.