A collection of pervasive street games is presented in this paper, that constitute a new social form of play taking place in public spaces, such as city parks, public spaces and streets. The main characteristic of these games is the ability to scale to a large number of players (in some cases involving more than 40 players) and can engage players located simultaneously in dispersed areas. Players interact with each other using a wide range of hardware devices that are either generic (such as smart phones) or specific (such as wireless sensor devices). We discuss a set of fundamental issues related to game design emphasizing on the one hand the interaction of the players with the ubiquitous computing environment and on the other hand the embedding of the game rules within the environment. The games are developed using open source technologies and evaluated in a series of events such as the Athens Plaython 2012 festival. The feedback received from the players indicates that this new form of gaming is indeed very promising.