Pathfinder Society scenarios are short, 4-hour adventures for use in Pathfinder Society Organized Play. Though they're designed for Pathfinder Society, they can easily be used for any game that uses the 3.5 or Pathfinder RPG rules.
Season 0 was the playtest season for Pathfinder Society Organized Play. It ran from August 2008 through July 2009 and used the 3.5 rules set of the world's oldest roleplaying game. Season 0 scenarios are still legal for play in Pathfinder Society. GMs may find that they need to make a few adjustments to make them fully compatible with the Pathfinder Roleplaying Game, but those changes should be minor.