Named is in some respects the archetypical PlayWorlds system, that emerged from decades of play and refinement. It is a fascinating look at how soft-touch you can make a game, while making those same touches robust enough to propel action and fun ever onward.
This is Named but Summarised and eminently playable of "hackable" to any world you want to play in.
The Wyrd System is a very simple event resolution mechanic that was designed with Play Worlds strongly in mind: a stripping back to simplicity that allows the world itself to be the driving force of the game.
The Unburied is a short horror adventure, where every word emanates from the world itself and the players (including the GM) are left to use that word as its base.