I had not heard of games of this genre before, but they are pretty exciting and I must thank Ulises Mejias for my first introduction to this medium. There are many definitions including the one here where ARGs are contrasted with serious games.
Apparently, the first such “game” dates back to 1996! Wikipedia defines it as “is an interactive narrative that uses the real world as a platform, often involving multiple media and game elements, to tell a story that may be affected by participants’ ideas or actions”.
Think of it as a dramatization parallel to the real world. The organizer, or Puppetmaster, starts by telling a story or leaving a cue, as in a puzzle. Real people and real technology are drawn in to real world dialogue and just like in real life, information is pieced together by the participants. The “game” word is a misnomer, really, because an ARG is very different than a game – in fact ARG creators follow the TINAG (This Is Not A Game) principle. Read about The Beast to get a deeper sense.
If you think of it, some aspects of the CCK08 course run by Stephen Downes and George Siemens in end-2008 resembled an ARG, in fact, hold true to the concept of sense-making in connectivism. I think a new analogy/metaphor of an educator could be the puppetmaster.