Characters are usually co-owned, but controlled by one player at a time. Losers in conflicts can earn story tokens that can be used to influence the game, so it's sometimes beneficial to play a supervillain that gets beaten to get more story tokens.
There is no GM. All the things the GM normally does are done by all the players. For example players create and play the villians who oppose other players heroes.
The game also has a gloating rule that emulates situations where (for example) the villain can easily kill the heroes, but won't.
Because players switch between co-owned characters and because players tend to play as if they were authors rather than actors some people argue that Capes and similar games should not be called RolePlaying games. In practice many, perhaps most, games are played with an agreement that certain characters will be played only by certain players.